Overnight Breakfast Casserole: Make-Ahead Dinner

This Overnight Breakfast Casserole is the ultimate make-ahead dinner-and-stay solution. It’s a hearty, savory bake of cubed bread, eggs, milk, cheese, and your choice of breakfast sausage or vegetables, assembled the night before and baked the next morning. It works beautifully because the overnight soak allows the bread to absorb the custard, resulting in a tender, soufflé-like texture that’s both satisfying and easy to serve to a crowd.

Ingredients

1 lb (450 g) breakfast sausage (or 2 cups / 200 g diced mushrooms for vegetarian)
1 tbsp (15 ml) olive oil, if using sausage or mushrooms
1 medium onion, diced (about 1 cup / 150 g)
1 red bell pepper, diced (about 1 cup / 150 g)
8 large eggs
2 cups (480 ml) whole milk
1 tsp (5 g) salt
1/2 tsp (1 g) black pepper
1 tsp (2 g) dry mustard powder (optional)
1 loaf (about 1 lb / 450 g) day-old crusty bread, cut into 1-inch (2.5 cm) cubes (about 10 cups / 400 g)
2 cups (200 g) shredded sharp cheddar cheese, divided
2 tbsp (8 g) chopped fresh parsley, for garnish (optional)

Instructions

Heat a large skillet over medium heat. Add the sausage and cook, breaking it up with a spoon, until browned and cooked through, about 8–10 minutes. If using mushrooms, heat the olive oil and cook the mushrooms until they release their liquid and start to brown, about 8 minutes. Transfer to a plate and set aside.
In the same skillet, add the onion and bell pepper. Sauté over medium heat until softened, about 5 minutes. Remove from heat.
In a large bowl, whisk together the eggs, milk, salt, pepper, and dry mustard (if using).
Add the bread cubes, cooked sausage (or mushrooms), sautéed vegetables, and 1 1/2 cups (150 g) of the shredded cheese to the egg mixture. Stir gently to combine, making sure all bread is coated.
Transfer the mixture to a greased 9×13-inch (23×33 cm) baking dish. Sprinkle the remaining 1/2 cup (50 g) of cheese on top. Cover with plastic wrap or foil and refrigerate overnight (at least 8 hours, up to 24 hours).
When ready to bake, preheat the oven to 350°F (175°C). Remove the casserole from the refrigerator and let it sit on the counter while the oven heats (about 20 minutes).
Bake uncovered for 50–60 minutes, until the center is set and the top is golden brown. The internal temperature should read 165°F (74°C) when checked with a food thermometer (USDA FSIS safe minimum for egg dishes).
Let rest for 10 minutes before slicing and serving. Garnish with parsley if desired.

Tips

Bread choice: Use a sturdy, slightly stale bread like sourdough, French, or Italian. Fresh, soft bread can turn mushy. If your bread is very fresh, toast the cubes in a 300°F (150°C) oven for 10 minutes before assembling.
Make it ahead: This casserole is designed to be assembled the night before. It can also be frozen (unbaked) for up to 1 month. Thaw overnight in the fridge before baking.
Don’t overmix: Stir gently to combine, but don’t mash the bread. Overmixing can make the casserole dense.
Check for doneness: The center should be just set—not jiggly. If the top browns too quickly, cover loosely with foil for the last 15 minutes of baking.

Serving Suggestions

Serve this casserole warm with a simple green salad dressed with lemon vinaigrette for dinner, or with fresh fruit and maple syrup for breakfast. It’s also great with a side of roasted potatoes or a dollop of sour cream and hot sauce.

Variations

Vegetarian: Skip the sausage and add 2 cups (200 g) of sautéed mushrooms and 1 cup (150 g) of chopped spinach (squeeze out excess moisture).
Southwest: Replace the cheddar with pepper jack, add 1 can (15 oz / 425 g) of drained black beans and 1 cup (150 g) of corn kernels.
Ham & Swiss: Use 1 1/2 cups (200 g) of diced ham and 1 1/2 cups (150 g) of Swiss cheese instead of sausage and cheddar.
Herb & Leek: Sauté 2 leeks (white part only, sliced) instead of onion and bell pepper, and add 2 tbsp (8 g) of fresh thyme or chives.

Storage and Reheating

Refrigerate leftovers in an airtight container for up to 4 days. To reheat, microwave individual portions for 1–2 minutes, or warm in a 350°F (175°C) oven for 10–15 minutes until heated through. The casserole can also be frozen after baking for up to 2 months; thaw overnight in the fridge and reheat as above.

Frequently Asked Questions

Can I use a different type of bread? Yes, any sturdy bread works—sourdough, French, Italian, or even whole wheat. Avoid very soft sandwich bread, which will become mushy.

Can I make this casserole without egg? You can try a flax egg substitute (1 tbsp ground flax + 3 tbsp water per egg), but the texture will be denser and less custardy. It’s better to use a tofu scramble for a vegan version.

How long can I keep the unbaked casserole in the fridge? The assembled casserole can be refrigerated for up to 24 hours before baking. Any longer and the bread may become too soggy.

Can I bake it immediately without refrigerating? Yes, you can bake it right away, but reduce the baking time by about 10 minutes. The overnight rest gives a better texture, but it’s not strictly necessary.

Why is my casserole watery? This can happen if you use too much milk or if your vegetables release a lot of water. Make sure to drain cooked mushrooms well and don’t add extra milk beyond the recipe.

Can I double this recipe? Absolutely. Use a larger baking dish (e.g., 11×15-inch) and increase the baking time by 10–15 minutes, checking for 165°F (74°C) in the center.

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Safety notes: safe minimum internal temperatures from USDA FSIS; raw and undercooked fish guidance from the U.S. FDA. Food safety notes

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