Make-Ahead Breakfast Casserole With Sausage and Peppers

I make this hearty breakfast casserole when the house is full, and I want one dish to handle the morning for me. Pork sausage gets browned until the edges catch, red and green bell peppers soften into sweet bites, and it all bakes with Gruyère and cheddar melted through the eggs into something golden and set on top. It’s sausage and cheese comfort food, and most of the work is done before it ever reaches the oven.

It’s the thing I lean on for slow holiday mornings, Christmas morning, and Thanksgiving morning especially, and for brunch with a crowd, because I can get most of it done the night before and just bake it off while the coffee goes on. It travels to a potluck without much fuss, and it feeds six from a single pan.

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I love making this for Thanksgiving morning, Christmas brunch, and Easter gatherings when I need something hearty that feeds a crowd. It’s also great for Mother’s Day and travels well to potlucks, and it’s something you can make ahead of time. It stays fresh in the fridge for 3 to 4 days or freezes for up to 3 months, and reheats easily in the oven or microwave, making it perfect for meal prep.

What You’ll Need

You’ll need all the ingredients shown in the photograph below.

Pork sausage. The savory backbone of the casserole, browned until the edges catch before anything else goes in. I use pork breakfast sausage, though turkey sausage works just as well if you’d rather go leaner.

Onion, red bell pepper, and green bell pepper. Diced and cooked down with the sausage until soft and sweet at the edges. If you’re out of fresh onion, onion powder covers it in a pinch.

Garlic. A couple of minced cloves for a warm, aromatic base. Garlic powder stands in if that’s what you have.

Salt and pepper. Basic seasoning, to taste. Seasoned salt is an easy swap if you want a little more going on.

Gruyère cheese. The one splurge here, melting nutty and smooth through the eggs. It’s the pricier cheese in the dish, so if it isn’t in the cart, leaning on more cheddar still makes a rich casserole.

Cheddar cheese. Half the shredded cheese gets mixed in and half goes on top, where it turns golden and bubbly in the oven.

Eggs. Half a dozen, whisked through everything to bind the casserole together as it bakes.

Chives and fresh parsley. Chopped and scattered over the top at the end for a fresh, bright finish against the rich base. Green onions stand in for the chives.

How to Make Breakfast Casserole

Scroll down for the full recipe instructions card containing a full printable recipe and measurements in both US customary and metric units.

Brown the sausage.

Heat the oven to 350°F (180°C) and set a large non-stick skillet over medium-high heat. Add the sausage and break it apart with a spoon as it cooks, until it’s browned all over, about 5 to 7 minutes. The browned bits carry a lot of the flavor.

Cook the vegetables.

Stir the diced onion, red and green pepper, minced garlic, salt, and pepper into the skillet. Keep cooking for 7 to 10 minutes, stirring now and then, until the vegetables are soft, the onion turns translucent, and the peppers caramelize a little at the edges.

Combine the mixture.

In a large bowl, combine the cooked sausage and vegetable mixture with the Gruyère, half of the shredded cheddar, and the eggs, whisking the eggs through so everything is evenly coated. This is the point to fold in any extras: a handful of shredded hash browns, diced potatoes, or pre-cooked diced ham to bulk it out, or a little pepperjack cheese for mild heat.

Assemble.

Grease a 9×13 baking dish with butter or cooking spray, then pour the mixture in and spread it into an even layer. Scatter the remaining cheddar over the top so it turns golden and bubbly as it bakes.

Bake.

Bake for 20 minutes, until the casserole is hot through, the center is set, and the cheese on top is golden brown at the edges. An egg casserole is cooked through when the center reaches 160°F.

Garnish and serve.

Let it rest for about 5 minutes so the eggs firm up and the slices hold together, then scatter the chopped chives (or green onions) and fresh parsley over the top. A few sliced green chiles add a spicy kick, or crumbled bacon for crunch, if you like.

Tips

• Use room-temperature eggs. Cold eggs don’t blend as smoothly, so let them sit out for about 10 minutes before mixing.
• Brown the sausage properly. Give it time to take on a deep color before the vegetables go in; that browning is where a lot of the savory flavor comes from.
• Add the garlic with the vegetables, not before. Garlic scorches fast on its own, so it goes in with the onion and peppers to stay sweet and aromatic.
•  Grease the dish well. Cheese likes to stick, so butter or spray every corner for cleaner slicing and washing up.
• Let it rest before slicing. Five minutes out of the oven lets the eggs set, so your slices hold together instead of sliding apart on the plate.
  

Make it Your Own

• Use turkey sausage. Swap the pork for turkey sausage if you’d rather go leaner; the method stays exactly the same.
• Lean on cheddar. Gruyère is the pricier cheese here, so if it isn’t on hand, using all cheddar still melts into a rich, savory casserole.
• Bulk it up for a crowd. Fold shredded hash browns, shredded potatoes, or frozen hash browns into the egg mixture to stretch the dish further and make it more filling for a big table.
  

What to Serve With Breakfast Casserole

This is a rich, savory dish, so I like something fresh alongside to balance it. Roasted vegetables, baked zucchini, mushrooms, or chopped broccoli add color and cut through the richness, and a simple green salad does the same. When I’m feeding a hungrier crowd, air-fried frozen hash brown potatoes, diced potatoes, or a pan of tater tot casserole round the table out. Toasted sourdough or buttery croissants are good for soaking up any loose egg, and a bowl of fresh fruit keeps things light. For a weekend brunch spread, it’s hard to beat next to strong coffee or a round of mimosas.

Make it Ahead

This is the part I rely on for a busy morning. Build the whole casserole up to the point where it’s spread in the dish, cover it tightly, and keep it in the fridge; then bake it fresh the next day. Because it’s made with raw eggs, assemble it and bake it within 24 hours rather than letting it sit longer than that. Let the dish stand on the counter while the oven heats, and give it a few extra minutes in the oven if it’s going in cold from the fridge. If it’s heading to a Christmas brunch or a potluck somewhere else, making it in a disposable aluminum pan keeps the cleanup easy.

How to Store Leftover Breakfast Casserole

Cool it first. Let the baked casserole cool completely, then cover it tightly with plastic wrap and foil, or move portions into an airtight container.

Refrigerate or freeze. In the fridge, baked leftovers keep for 3 to 4 days. To hold them longer, cut the casserole into portions, wrap each tightly, and freeze for up to 3 months. Thaw frozen portions overnight in the fridge before reheating.

Reheat. These are already-baked leftovers, so you’re warming them back through, not cooking them from raw. Reheat individual portions in the microwave, or warm the entire dish covered with foil in a 350°F oven, until it’s steaming hot all the way through, to an internal temperature of 165°F.

Serving it at a potluck or gathering? It travels well, but cooked food shouldn’t sit out at room temperature for more than 2 hours, or 1 hour if it’s a hot day above 90°F. Keep it covered and get leftovers back in the fridge inside that window.

Making It Go Further

1. One pan, several meals. A single 9×13 covers a holiday breakfast and still sends leftovers to the next few mornings.
2. Get ahead of a busy week. Because it holds and reheats well, it doubles as make-ahead breakfast meal prep, portioned out for grab-and-go mornings.
3. Cook once, freeze for later. Portion and freeze what you won’t get through that week for a fast breakfast down the line.

More Casseroles to Try

If this classic breakfast casserole earns a spot in your rotation, these are the other one-dish casseroles I come back to, each a big, comforting bake that’s just as good over the holiday season as on a slow weekend, with not much to wash up after.

•  Chicken Casserole is where I go on the nights I’d rather cook with chicken.
• Cowboy Casserole is my pick when I want another hearty, crowd-sized bake.
• Chili Relleno Casserole leans cheesy and pepper-forward for a change of pace.
• Tuna Casserole is the creamy, pantry-friendly one for a low-effort dinner.