Christmas Breakfast Casserole

Sausage, Mushroom, Bell Pepper & Egg Breakfast Casserole

Christmas morning isn’t the time to start chopping. This make-ahead breakfast bake—sausage, mushrooms, red bell pepper, potato, sage, and cheddar—comes together the day before, then chills overnight.

In the morning, bring to room temp and bake until just set with a golden top. Pre-cooking the vegetables keeps the casserole from going watery, and the egg-to-dairy ratio gives a sliceable, creamy interior.

Watch my video to follow along step-by-step.

Christmas Breakfast Casserole

Yield: 4 servings
Prep: 25 minutes (active)
Chill: 8–24 hours (overnight)
Bake: 35–45 minutes
Oven: 350°F (180°C)

Ingredients

• 12 oz (340 g) pork sausage, casings removed

• 8 oz (225 g) mushrooms, sliced

• 2 Tbsp (28 g) unsalted butter

• 1 medium potato (about 10 oz / 280 g), peeled and small-diced (¼–½ in / 6–12 mm)

• 1 large red bell pepper, small-diced

• 1–2 Tbsp fresh sage, chopped (plus extra for garnish)

• 1 cup (100 g) grated cheddar (or Gruyère)

• 5 large eggs

• 1 cup (240 ml) whipping cream (or half-and-half)

• ¾ tsp fine sea salt, divided (adjust if sausage is salty)

• ½ tsp freshly ground black pepper

To prep the dish:
Butter for greasing a 10×7 in (26×18 cm) ovenproof dish; foil for covering

Method

1. Brown the sausage & mushrooms. Heat a large skillet over medium-high. Cook sausage, breaking it up, until browned. Add mushrooms and sauté until their liquid evaporates and edges take on color. Transfer both to a large bowl; set aside.

2. Pan-roast the potato & pepper. In the same skillet, melt the butter. Add the diced potato and cook, stirring, until lightly golden on the edges. Add bell pepper and a pinch of sea salt. Cover and cook 8–10 minutes, stirring occasionally, until the pepper softens and the potato is just tender (add a tablespoon of water if the pan looks dry).

3. Add sage; combine & cool. Stir in the chopped sage and cook 30–60 seconds until fragrant. Transfer the potato mixture to the bowl with the sausage and mushrooms. Toss to combine and let cool to room temperature.

4. Build the dish. Butter your baking dish. Sprinkle in the shredded cheese. Add the cooled sausage vegetable mixture on top and spread evenly.

5. Make the custard. In a bowl or measuring jug, whisk the eggs, cream, remaining sea salt, and black pepper until smooth. Pour evenly over the dish and tap gently to settle.

6. Cover & chill. Cover tightly with foil and refrigerate 8–24 hours.

7. Bake. Remove from the fridge 20–30 minutes while you preheat the oven to 350°F (180°C). Bake covered for 25 minutes, then check. If the center is still quite wobbly, continue covered 5–10 minutes. Uncover and bake a further 5–15 minutes until the top is lightly browned and the center is just set (a gentle wobble is fine). Internal temp should reach about 165°F (74°C).

8. Rest & serve. Let stand 10 minutes, then slice and serve. Garnish with a little extra sage if you like.

Make-Ahead & Scaling

• Make-ahead: Assemble fully and chill 1 day ahead.

• Bigger batch: Double into a 13×9 in (33×23 cm) pan; add 10–15 minutes to the covered bake and watch the center.

• Reheat: Cover and warm leftovers at 325°F (165°C) for 10–15 minutes, or microwave gently.

Swaps & Add-Ins

• Cheese: Gruyère, Monterey Jack, or Colby.

• Dairy: Half-and-half or whole milk; bake to just-set.

• Extras: Green onion, sautéed spinach, or a dash of hot sauce..

Larder Notes

• Leftovers: Cover and refrigerate up to 3 days. Reheat covered at 325°F for 10–15 minutes, or microwave gently. Freezes well in portions.

• Diet tweaks: Pork-free? Use chicken/turkey sausage. Vegetarian? Skip sausage; add 8–10 oz (225–285 g) sautéed spinach or extra mushrooms.

• Oven modes: Conventional 350°F. Fan/convection: 325–340°F and start checking 5 minutes earlier..

• Troubleshooting: Still loose? Cover and bake 5–10 more minutes. Pale top? Uncover for the last 10 minutes or hit with broiler briefly.

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