Winter Brunch Egg Casserole

The kitchen was still dark when I started prep, snow falling past the window in those fat, quiet flakes that make everything feel muffled and calm. I'd promised to bring brunch to my sister's place, and this egg casserole was the only thing that felt substantial enough for a day that demanded something warming. The smell of onions hitting butter in the pan filled the whole apartment, and I remember thinking how winter cooking has this particular quality—everything feels slower, more intentional, like you're building a tiny fortress against the cold outside.

My friend Sarah brought this recipe back from a weekend at her family's lake house, originally scribbled on the back of a grocery receipt. We made it for a New Year's Day brunch years ago, and someone—maybe me, probably me—burned the top because we got too caught up in mimosas and conversation. Everyone still went back for seconds, picking around the dark corners, and I learned that a slightly overdone casserole is still better than no casserole at all.

Ingredients

• 1 medium onion, diced: Sweet onions work beautifully here, but whatever you have in your pantry will do the job just fine
• 1 red bell pepper, diced: The red variety adds such lovely color against the golden cheese, and they're sweeter than green peppers
• 1 cup baby spinach, chopped: Fresh spinach wilts down into almost nothing, so don't be shy about adding a bit more if you want extra greens
• 1 cup cremini or white mushrooms, sliced: Cremini mushrooms have a deeper, earthier flavor that stands up well to the rich custard
• 1 ½ cups shredded cheddar cheese: Sharp cheddar gives you that tangy bite that cuts through all the creamy richness
• 1 cup whole milk: I've tried lower fat versions and honestly, they just don't give you the same silky texture
• ½ cup heavy cream: This is what transforms it from ordinary egg bake into something that feels restaurant special
• 8 large eggs: Room temperature eggs will incorporate more smoothly into the dairy mixture
• 4 cups rustic bread, cut into 1-inch cubes: Day old bread actually works better than fresh—it absorbs the custard without turning to mush
• 1 tsp salt: Depending on your cheese, you might want to start with less and adjust to taste
• ½ tsp black pepper: Freshly cracked makes such a difference in the final flavor profile
• ½ tsp dried thyme: Thyme has this cozy, woodsy flavor that screams winter comfort food
• ¼ tsp smoked paprika: Just enough to add a subtle depth without making it taste like barbecue
• ½ cup cooked breakfast sausage or bacon, crumbled: If you're going the meat route, cook it until crispy so it maintains texture in the bake
• 2 tbsp chopped fresh parsley: Mostly for looks, but that pop of green on a golden casserole is worth the extra chop

Instructions

Get your oven ready:

Preheat to 350°F (175°C) and give your 9x13-inch baking dish a thorough coating with butter or cooking spray

Sauté your vegetables:

Heat butter in a large skillet over medium heat, cook onion and bell pepper 4 to 5 minutes until they start to soften, add mushrooms for another 3 minutes, then stir in spinach until it wilts completely

Whisk the custard base:

In a large bowl, beat together eggs, milk, cream, salt, pepper, thyme and smoked paprika until the mixture is completely uniform

Combine everything:

Add bread cubes, sautéed vegetables, half the cheese and optional meat to the egg mixture, folding gently until every piece of bread is coated

Assemble and top:

Pour the mixture into your prepared dish and scatter the remaining cheese across the top in an even layer

Bake until golden:

Slide into the oven for 40 to 45 minutes until the center is set and the cheese has formed this gorgeous golden crust

Rest before serving:

Let it cool for at least 10 minutes so the custard sets properly, then sprinkle with parsley and slice while still warm

Save Pin

Last December, I made this for a brunch that ended up lasting well into dinner. People kept wandering back into the kitchen, grabbing just one more square, and eventually we just accepted that this casserole was the whole day's plan. There's something about a dish that can anchor an entire gathering that makes me feel like maybe I've figured out this hosting thing after all.

Make Ahead Magic

I've learned through experience that having the components prepped the night before transforms brunch from stressful to genuinely enjoyable. The vegetables can be sautéed and stored in the fridge, and the bread can be cubed and left out on the counter to get even more stale. Morning you will be so grateful for the preparation that past you put in.

Cheese Swaps

While cheddar is classic, gruyère creates this incredible nutty depth that feels downright fancy. If you're serving people who swear they don't like breakfast casserole, try half gruyère and half sharp cheddar—it might just change their minds entirely about what egg dishes can be.

Serving Suggestions

A crisp green salad with an acidic vinaigrette cuts through the richness beautifully. If you want to round out the table, consider some roasted potatoes or fresh fruit on the side. And for drinks, something bubbly feels right, whether that's mimosas or sparkling cider.

• Cut the casserole into squares before bringing it to the table—it serves more neatly that way
• Have hot sauce available for guests who like extra heat with their eggs
• The leftovers actually reheat surprisingly well in the microwave, though you'll lose some of that golden crust

Save Pin

Winter mornings deserve something that warms you from the inside out, and this casserole never fails to deliver exactly that. Hope it becomes part of your own cold weather traditions.

Recipe FAQs

→ Can I prepare this the night before?

Yes, assemble everything in the baking dish, cover tightly, and refrigerate overnight. Add 10-15 minutes to the baking time if cooking from cold.

→ What bread works best for this casserole?

Day-old rustic bread, sourdough, or French bread hold up beautifully. Slightly stale cubes absorb the egg mixture without becoming mushy during baking.

→ Can I make it vegetarian?

This version is already vegetarian. Simply omit the optional sausage or bacon. The vegetables and cheese provide plenty of savory flavor and protein.

→ How do I know when it's done baking?

The center should be set and not jiggly when you gently shake the pan. The top will be golden brown with melted cheese, and a knife inserted in the center comes out clean.

→ Can I freeze leftovers?

Yes, individual portions freeze well for up to 2 months. Thaw overnight in the refrigerator and reheat at 350°F until warmed through.

→ What vegetables can I substitute?

Try diced zucchini, chopped kale, or caramelized roasted vegetables. Just cook them slightly before adding to ensure proper texture in the finished dish.