Easy, Make-Ahead Chicken Sausage Breakfast Casserole
Golden on top and soft and custardy underneath, this overnight breakfast casserole is packed with spicy chicken sausage, peppers, and onions in every bite. Assemble it before bed, and breakfast for a crowd is already halfway done.
This overnight chicken sausage breakfast casserole is a filling choice for holiday mornings, weekend brunches, or anytime a house full of hungry guests needs to be fed. It makes enough to feed a crowd from one 9×13-inch dish, giving you more time to chat with guests over coffee instead of standing at the stove taking individual egg orders.
For more alpha-gal friendly breakfast ideas, check out my baked eggs Florentine, smoked salmon omelet, and dairy-free tofu pancakes.
Before We Get to the Good Stuff
Medical disclaimer: The information provided on Sage Alpha Gal is based on my personal experience living with alpha-gal syndrome. Although I cite and link to expert sources, nothing published here is medical advice. Because alpha-gal sensitivities vary by person, my alpha-gal is not necessarily your alpha-gal, so be sure you understand your dietary restrictions and work with your healthcare provider as needed.
Affiliate disclosure: Sage Alpha Gal is a reader-supported site, and this post may contain affiliate links. If you make a purchase through one of these links, I may earn a teeny tiny commission at no additional cost to you. That income helps offset the costs of running this site. You can read all of the legal blah blah blah (as my little niece says) on the full disclosure page.
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Why You’ll Love This Recipe
- Full of savory flavor. Spicy chicken sausage, sautéed peppers and onions, Italian seasoning, and melty dairy-free cheddar make every bite count.
- Built from familiar ingredients. Eggs, bread, sausage, vegetables, plant-based milk, and a few pantry seasonings do most of the work.
- Easy to customize. Choose mild or spicy sausage, change the bell pepper, or use the dairy-free cheese and bread you prefer.
- Mostly hands-off after assembly. Once the casserole is layered and chilled in the fridge overnight, the oven handles the rest.
- Works beyond breakfast. Serve it for brunch, lunch, or an easy breakfast-for-dinner night.
Key Ingredients and Easy Swaps
This filling casserole gets its savory flavor from a short list of familiar ingredients. Here’s what each key ingredient brings to the dish, along with the swaps that work best.
Chicken Sausage
Spicy ground chicken sausage gives this casserole its savory backbone. For less heat, use mild chicken sausage. Turkey sausage, duck sausage, or another alpha-gal friendly option can also work.
When choosing an alpha-gal-friendly sausage, check the casing as carefully as the filling. Chicken, turkey, or duck sausage may be stuffed into pork or another mammal-derived casing. Simply slitting and discarding that casing does not make the sausage safe because the filling has already been in direct contact with it, so choose bulk sausage or a product with a casing that works for your sensitivities.
Bell Pepper and Onion
Bell pepper and onion add color and a little sweetness. Cook them with the sausage until softened, then drain the mixture well so extra moisture does not end up in the egg custard.
Eggs
Twelve large eggs form the base of the custard. They help hold the sausage, vegetables, cheese, and bread together as the casserole bakes.
Plant-Based Milk
Four cups of plant-based milk turn the eggs into a soft custard that soaks into the bread overnight. I used full-fat oat milk for a richer texture. Choose a plain, neutral-flavored variety rather than vanilla or another sweetened flavor.
Dry Mustard and Italian Seasoning
Dry mustard adds gentle warmth without making the casserole taste like mustard. Italian seasoning brings together the sausage, peppers, onions, and cheese with one easy pantry blend.
Sage Advice: No Italian seasoning in the pantry? Combine dried basil, oregano, thyme, rosemary, and marjoram, then use two teaspoons in the casserole. My homemade Italian seasoning recipe has the exact proportions.
Dairy-Free Shredded Cheese
I recommend Violife Just Like Cheddar Shreds. Other dairy-free shreds can work, but melting and flavor vary by brand. If you tolerate dairy, regular shredded cheddar is an easy substitute.
Bread
Cubed bread absorbs the egg mixture overnight and gives the casserole its soft, custardy structure. A sturdy loaf will hold its shape better, while very soft bread creates a more pudding-like texture. If you use gluten-free bread, choose a firm loaf and expect the finished texture to vary by brand.
Scroll down to the recipe card for a complete list of ingredients and the amounts needed to make this dish.
How to Make Overnight Chicken Sausage Breakfast Casserole
A little prep the night before makes it easy to get this overnight breakfast casserole on the table the next morning. Here’s what you do:
- Cook the filling. Brown the chicken sausage with the diced bell pepper and chopped onion, then drain the mixture on a paper towel-lined plate.
- Mix the custard. Beat the eggs in a large bowl, then whisk in the plant-based milk, dry mustard, Italian seasoning, salt, and pepper.
- Build the base. Coat a 9×13-inch baking dish with olive oil spray and spread the cubed bread evenly across the bottom.
- Add the remaining layers. Spoon the sausage mixture over the bread, sprinkle the dairy-free cheese on top, and pour the egg mixture evenly over everything.
- Chill overnight. Cover the baking dish and refrigerate it until the next morning.
- Bake the casserole. Bake uncovered at 350°F for 45 to 50 minutes, until the center is mostly set. Increase the oven temperature to 400°F and bake for another 5 to 10 minutes, until the top is golden brown.
You can find step-by-step instructions in the recipe card below.
Can I Make This Chicken Sausage Breakfast Casserole Ahead?
Yes. This recipe is designed to be assembled the night before, covered, and refrigerated until morning. That overnight rest gives the bread time to absorb the seasoned egg mixture, so the casserole bakes into a soft, cohesive dish instead of separate layers of bread and egg.
Because the assembled casserole contains raw eggs, treat it as a perishable dish. USDA guidance says to cook it the morning or day after assembly and not to freeze it uncooked. Keep it covered and refrigerated until you are ready to bake it.
Tips for the Best Results
This overnight breakfast casserole is forgiving, but moisture and timing still matter. These small details help the bread soak evenly, the eggs set properly, and the top turn golden without drying out.
- Cook and drain the filling thoroughly. Excess moisture from the sausage, pepper, or onion can make the finished casserole watery.
- Cut the bread into similar-size cubes. Even pieces absorb the custard at roughly the same rate and bake more consistently.
- Use plain plant-based milk. Vanilla or strongly sweetened milk can pull this savory casserole in a very strange direction.
- Distribute each layer evenly. Spread the bread, sausage mixture, cheese, and egg custard from edge to edge so every serving gets a little of everything.
- Watch the final high-heat finish closely. Once the oven reaches 400°F, begin checking at five minutes so the top turns golden without becoming too dark.
What to Serve with Overnight Breakfast Casserole
This casserole already brings eggs, sausage, bread, vegetables, and cheese to the table, so the sides can stay simple. Fresh berries, sliced melon, citrus fruit salad, or a lightly dressed green salad add a cool, fresh contrast to the warm, savory casserole.
For a larger brunch spread, add roasted breakfast potatoes, muffins, or pancakes. My sheet pan pancakes are another easy way to feed a crowd without flipping batch after batch at the stove.
How to Store Leftover Overnight Breakfast Casserole
Refrigerate leftovers within two hours of serving. Cut the casserole into portions and store them in a shallow airtight container in the refrigerator for three to four days, following USDA guidance for handling leftovers.
Reheat individual slices in the microwave or warm several portions in a covered baking dish until the center reaches 165°F. For longer storage, freeze the baked casserole in individual portions for about three months. Thaw frozen slices overnight in the refrigerator before reheating.
Frequently Asked Questions About Overnight Breakfast Casserole
Can You Freeze This Overnight Breakfast Casserole?
Yes, but bake it first. Let the baked casserole cool, cut it into portions, wrap them well, and freeze for about three months. Thaw overnight in the refrigerator and reheat to 165°F.
Can You Skip the Overnight Step?
Yes, although the texture may be less custardy because the bread has less time to absorb the egg mixture. If possible, refrigerate the assembled casserole for at least an hour before baking.
Should Breakfast Casserole Be Covered While Baking?
Bake this casserole uncovered so the top can brown. If the top becomes dark before the center reaches 160°F, tent the dish loosely with foil and continue baking until the middle is done.
More Mammal-Free Breakfast Recipes
For even more inspiration, browse my full collection of alpha-gal friendly breakfast recipes.
Chicken Sausage Breakfast Casserole
Equipment
- Wooden spoon or spatula
- Large mixing bowl
- Cutting board and chef’s knife
- Measuring cups and spoons
Ingredients
- 1 lb spicy ground chicken sausage
- 1 bell pepper, diced
- 1 onion, finely chopped
- 12 large eggs
- 4 cups plain neutral-flavored plant-based milk (I used full-fat oat milk)
- 2 tsp dry mustard
- 2 tsp Italian seasoning
- salt and pepper, to taste (I used 1 tsp salt and ½ tsp black pepper)
- olive oil cooking spray
- 4 cups cubed bread (about 6 to 8 slices)
- 8 oz dairy-free shredded cheddar cheese (I recommend Violife Just Like Cheddar or Violife Mexican Style Shreds)
Instructions
- Heat a large skillet over medium heat. Add the chicken sausage, bell pepper, and onion. Cook, breaking up the sausage, until the vegetables are softened and the sausage reaches 165°F, 8 to 10 minutes. Transfer the mixture to a paper towel-lined plate to drain.
- In a large bowl, beat the eggs. Whisk in the plant-based milk, dry mustard, Italian seasoning, salt, and black pepper.
- Coat a 9×13-inch baking dish with olive oil spray. Spread the bread cubes evenly across the bottom.
- Spoon the sausage mixture evenly over the bread cubes.
- Sprinkle the dairy-free cheese evenly over the sausage mixture.
- Pour the egg mixture evenly over the layers. Cover tightly and refrigerate for 8 to 12 hours.
- When ready to bake, remove the casserole from the refrigerator and let it sit at room temperature while the oven preheats to 350°F.
- Uncover and bake for 45 to 50 minutes, until the center is nearly set. Increase the oven temperature to 400°F and bake for another 5 to 10 minutes, until the top is golden brown and the center reaches 160°F. Let the casserole rest for 10 minutes before slicing.
Notes
- Check sausage casings as carefully as the filling. Poultry sausage may be stuffed into pork or another mammal-derived casing. Removing the casing does not eliminate the cross-contact risk, so choose bulk sausage or a product with a casing that works for your sensitivities.
- Can’t find alpha-gal-friendly bulk sausage? Season ground chicken or turkey with black pepper, salt, dried parsley, Italian seasoning, garlic powder, red pepper flakes, and thyme as it browns.
- Use plain, neutral-flavored plant-based milk. Vanilla or sweetened varieties can make this savory casserole taste oddly sweet.
- Cover and refrigerate the assembled casserole for 8 to 12 hours, then bake it the next morning or day after assembly. Do not freeze the casserole uncooked.
Nutrition
Please Note: Nutrition information is automatically calculated. It should only be used as an approximation.
No Artificial Intelligence
Every recipe I share has been cooked in my kitchen, photographed by me, and taste tested by my very patient family. No AI-generated slop here! If it’s on Sage Alpha Gal, it’s because I made it, loved it, and would gladly put it on my table again.
