Overnight Breakfast Casserole for a Crowd (Feeds 12)

This breakfast casserole feeds 12 and does all its work the night before: 15 minutes of assembly, an overnight rest in the fridge, and a 50-minute hands-off bake in the morning. Bread, sausage, cheese, and a dozen eggs soak together overnight so the whole thing bakes up like a savory bread pudding — puffed, golden, custardy in the middle. You wake up, turn on the oven, and make coffee while breakfast cooks itself.

This is our Christmas-morning, houseguest, and team-brunch recipe, and the overnight rest isn’t just convenient — it’s what makes the casserole good. We’ve tested same-day versions; they’re fine. The overnight pan is the one people ask about.

Ingredients (one 9x13 pan, serves 12)

• 1 lb breakfast sausage (or diced ham, or 12 oz bacon, cooked)
• 8 cups cubed sturdy bread (a day-old French loaf or sourdough — about 1 large loaf)
• 2 1/2 cups shredded sharp cheddar, divided
• 12 large eggs
• 2 1/2 cups whole milk
• 1 tsp Dijon mustard
• 1 tsp kosher salt, 1/2 tsp black pepper
• 2 green onions, sliced (optional)

The night before (15 minutes)

1. Brown the sausage, breaking it up, and drain. (Using ham? No cooking needed — this becomes a 10-minute job.)
2. Layer the bread cubes in a greased 9x13, then the sausage, then 2 cups of the cheese.
3. Whisk the eggs, milk, mustard, salt, and pepper, and pour evenly over everything. Press the bread down gently so it starts drinking.
4. Cover and refrigerate 8–24 hours.

That overnight soak is the technique: the custard fully saturates the bread, so it bakes into one cohesive, sliceable casserole instead of scrambled eggs sitting on croutons. It’s the same assemble-ahead logic that makes ham and cheese sliders our favorite party food — the fridge does the work while you sleep.

In the morning (hands-off)

1. Pull the pan out while the oven heats to 350°F — a 20-minute counter rest helps it bake evenly.
2. Top with the remaining 1/2 cup cheese and the green onions.
3. Bake uncovered 45–55 minutes, until puffed, golden, and set. A knife in the center should come out without wet egg, or an instant-read thermometer should read 160°F in the middle.
4. Rest 10 minutes before slicing into 12 squares. It slices cleaner after the rest, and it stays hot far longer than you’d think.

If the top browns before the center sets, tent loosely with foil for the last 15 minutes.

Timeline for a 9:00 am brunch

When	What
Night before, 9:00 pm	Assemble, cover, refrigerate (15 min)
7:40 am	Casserole on the counter, oven to 350°F
8:00 am	Into the oven
8:50 am	Check for doneness; rest 10 min
9:00 am	Slice and serve, still hot

Round out the table with fruit and something bready — a waffle bar made from pancake mix converted to waffles is our go-to pairing, and both scale to the bigger spreads on our easy meals for a group list.

Swaps and scaling

• Meatless: swap the sausage for 2 cups of sautéed mushrooms and a handful of spinach (squeeze it dry first — water is the enemy of custard).
• Feeding 20+: two pans bake side by side with no time change. Assemble both the night before.
• Freezer option: assemble, freeze unbaked up to a month, thaw 24 hours in the fridge, then bake as directed — a natural graduate of our freezer meal prep system.
• Bread matters: soft sandwich bread turns mushy. Day-old French, sourdough, or even leftover dinner rolls hold their structure through the soak.

FAQ

How long can breakfast casserole sit in the fridge before baking?

Between 8 and 24 hours is the sweet spot — long enough for the bread to fully absorb the custard. Past 24 hours the bread can over-soften, so if plans change, bake it and reheat slices instead.

Why is my breakfast casserole soggy in the middle?

Usually one of three things: under-baking (the center needs to hit 160°F), watery add-ins like unsqueezed spinach or fresh tomatoes, or soft bread that collapsed in the soak. Sturdy day-old bread and a full 45–55 minute bake solve it.

Can you bake breakfast casserole right away instead of overnight?

Yes — let it sit 30 minutes on the counter so the bread absorbs some custard, then bake as directed. The texture is slightly less unified than the overnight version, but it works when plans are last-minute.

How many people does a 9x13 breakfast casserole feed?

Twelve solid squares as part of a brunch spread with fruit and pastries, or 8 generous portions if it’s the whole meal. For a bigger crowd, make two pans — they bake side by side in the same 50 minutes.