Cheesy Sausage and Spinach Christmas Breakfast Casserole

This christmas breakfast casserole comes out golden-brown and bubbling in 70 minutes, all crispy sausage and melty cheddar. Assemble it the night before, and Christmas morning is just oven and coffee. It feeds ten for an easy holiday brunch.

Day-old bread drinks up the custard without turning to mush. Baking under foil sets the center gently, then uncovering lets the cheddar puff up golden-brown and bubbling.

Ingredients You'll Need

Unsalted Butter: Softened butter is your nonstick insurance policy and your first layer of flavor. Rubbed into every corner, it helps the edges turn golden and lets squares lift out cleanly. No butter? A thin swipe of neutral oil or nonstick spray works fine.

Ground Breakfast Sausage: This is the savory heart of the dish, already seasoned with sage and black pepper. Browned into crisp, golden crumbles, it gives every bite a salty, meaty crunch. Swap in ground turkey sausage, or crumbled chorizo if you like a little heat.

Yellow Onion: A small yellow onion, finely diced, melts into sweet, translucent bits. It quietly rounds out the sausage so the filling tastes deep, not just salty. A shallot or two makes a gentle, slightly more delicate stand-in.

Red Bell Pepper: Diced red pepper brings juicy sweetness and festive red flecks. My daughter calls them "Christmas confetti," and honestly, she's right. Orange or yellow peppers taste nearly the same, and a green one adds a grassier bite.

Baby Spinach: Roughly chopped spinach wilts down into soft, dark green ribbons. It adds color, freshness and a little earthy balance to all that cheese. Chopped kale works too, but give it an extra minute in the pan.

Day-Old French Bread: Slightly stale bread is the secret structure here. Its dry, open crumb drinks up the custard like a sponge but still holds its shape. Sourdough or challah are lovely swaps. Just cube them and let them dry out overnight.

Sharp Cheddar Cheese: Sharp cheddar holds its own against sausage and egg with tangy, bold flavor. Shredding it yourself means a silky, even melt and a bubbly, golden top. Gruyère, Monterey Jack or a smoked gouda would all be delicious here.

Large Eggs: Ten eggs build the custard that sets everything into tender, sliceable squares. Room-temperature eggs whisk smoother and bake more evenly, with no rubbery spots. For a lighter dish, swap a few whole eggs for liquid egg whites.

Whole Milk: Whole milk keeps the custard creamy and soft instead of spongy. Its fat makes each bite taste rich without feeling heavy. Half-and-half makes it extra luxurious, and unsweetened oat milk works for dairy-free mornings.

Dijon Mustard: Just one teaspoon, and you won't taste mustard at all. It quietly sharpens the cheese and helps the custard taste bright and balanced. A pinch of dry mustard powder or a little whole-grain mustard does the same job.

Kosher Salt: Kosher salt seasons the custard so the eggs and bread don't taste flat. Its coarse flakes dissolve easily and are hard to overdo. Using fine table salt? Use about half as much.

Black Pepper: Freshly ground pepper adds gentle warmth and tiny dark specks to the pale custard. Grinding it fresh makes it fragrant, not dusty. White pepper is a mild, invisible swap if you prefer.

How to Make It (Step by Step)

It all comes together in one skillet and one baking dish: brown the sausage and veggies, soak the bread in custard, then bake until golden-brown and bubbling.

Even if you've never made a breakfast casserole before, this one is forgiving, and you'll pull out a puffy, cheesy beauty.

1. Preheat your oven and rub the softened butter over the bottom and sides of a 9x13-inch baking dish until every corner gleams, 2-3 minutes at 350°F / 175°C. A paper towel spreads it thin and even.

2. Brown the ground breakfast sausage in a large skillet, breaking it into small crumbles with a wooden spoon. Cook until no pink remains and the edges turn crisp and golden-brown, 7-9 minutes at medium-high heat (400°F / 200°C).

3. Stir the diced onion and red bell pepper into the sausage. Cook until the onion turns translucent and the kitchen smells sweet and savory, 4-5 minutes at medium heat (350°F / 175°C).

4. Fold in the chopped baby spinach and keep stirring until it collapses into soft, dark green ribbons, 1-2 minutes at medium heat (350°F / 175°C). Pull the pan off the heat.

5. Spread the bread cubes in the buttered dish, then scatter the sausage mixture and 1½ cups of cheddar over them. Toss gently until everything looks evenly speckled, 2-3 minutes at room temperature (70°F / 21°C).

6. Whisk the eggs, milk, Dijon, kosher salt and black pepper in a large bowl. Keep going until the custard turns smooth and pale yellow with no streaks, 1-2 minutes at room temperature (70°F / 21°C).

7. Pour the custard slowly over the bread and press the cubes down with a spatula. Let it soak until the bread feels heavy and saturated, 10-15 minutes at room temperature (70°F / 21°C). Overnight in the fridge works beautifully too.

8. Cover the dish tightly with foil and bake until the edges start to bubble softly, 30 minutes at 350°F / 175°C. The foil keeps the top from browning too early.

9. Uncover, sprinkle on the last ½ cup of cheddar, and bake until puffed, golden-brown and bubbling. A knife in the center should come out clean, 15-20 minutes at 350°F / 175°C.

10. Rest the casserole until the custard firms up and slices cleanly, 10 minutes at room temperature (70°F / 21°C). Then cut squares and watch everyone come running.

Leftovers keep four days chilled or three months frozen, so reheat slices covered at 350°F. Swap sourdough for French bread if needed, but skip pre-shredded cheddar, which melts grainy instead of velvety.

Serving size: 1 portion · Calories: 410 · Total Fat: 26g · Saturated Fat: 11g · Carbs: 20g · Fiber: 1g · Sugar: 4g · Protein: 23g · Sodium: 890mg

Tips and Tricks

• Equipment: Use a 9x13-inch ceramic or glass baking dish: Thick walls heat gently and evenly, so the custard sets without scorching. A thin metal pan can overcook the edges before the center catches up.
• Temperature precision: Let the oven fully reach 350°F / 175°C first: A cold oven starts the custard sluggishly and leaves it weepy. Give it a full preheat, then trust the clean-knife test in the center.
• Common mistake: Pouring the custard too fast: Dump it all at once and it pools at the bottom while the top cubes stay dry and toasty-hard. Pour slowly in a circle. Then press every cube down with a spatula until it feels heavy and saturated.

• Flavour upgrade: Add a pinch of smoked paprika to the custard: Just ¼ teaspoon whisked in with the Dijon makes the custard taste quietly smoky. It hugs the sausage like a warm wool scarf on Christmas morning.
• Texture tip: Uncover for that puffed, golden top, then rest it: The foil keeps the center tender. Pulling it for the last 15-20 minutes lets the cheddar blister golden-brown and bubbly. Then wait the full 10 minutes so each square slices clean and custardy.

Frequently Asked Questions

Can I make this christmas breakfast casserole gluten-free without it turning soggy?

Use 8 cups of cubed gluten-free sandwich bread, toasted 10 minutes at 350°F to dry it out, and cut the milk to 2 cups since gluten-free bread absorbs less. Check that your sausage and Dijon are labeled gluten-free too.

Can I freeze the assembled casserole unbaked to get ahead of Christmas week?

Yes, wrap the unbaked dish tightly in plastic and foil, freeze it up to 1 month, then thaw it in the fridge for 24 hours. Bake covered at 350°F for 10-15 minutes longer than usual, since the custard starts cold.

Why is my breakfast casserole soggy and wet in the center after baking?

The bread was likely too fresh or the spinach released moisture, so use truly day-old cubes and cook the spinach until no liquid pools in the skillet. If the center jiggles, bake uncovered another 5-10 minutes until a knife comes out clean, then rest it a full 10 minutes.

What to Serve With This

• Citrus Pomegranate Salad: Juicy orange segments and ruby pomegranate seeds cut through the rich sausage and cheddar like a bright, tangy wake-up call.
• Lemony Arugula Salad: Peppery arugula in a sharp lemon vinaigrette brings a fresh, crisp bite against the soft, custardy bread.
• Blistered Cherry Tomatoes: Warm, burst tomatoes add sweet-tart juice that loves the savory sausage and melty cheese.
• Greek Yogurt with Berries: Cool, tangy yogurt and tart berries give a creamy, refreshing break between cheesy bites.