Overnight Sausage, Spinach, and Gruyère Breakfast Strata

Why You’ll Love This Recipe

• Hands-off morning: assemble the night before, then just bake.
• Balanced flavors: sweet caramelized onions, savory sausage, melty Gruyère, and tender spinach.
• Custardy inside, crisp golden top—classic strata texture.
• Feeds a crowd and reheats beautifully for weekday breakfasts.

Grocery List

• Produce: 2 yellow onions, 2 garlic cloves, 5 oz baby spinach, fresh thyme, chives or parsley (garnish)
• Dairy: 10 large eggs, whole milk, half-and-half, Gruyère, Parmesan, unsalted butter
• Pantry: 1 lb crusty bread, olive oil, Dijon mustard, ground nutmeg, kosher salt, black pepper, red pepper flakes (optional), breakfast sausage (12 oz)

Full Ingredients

For the Caramelized Onions

• 2 medium yellow onions (about 1 lb), thinly sliced
• 2 tbsp unsalted butter
• 1 tbsp olive oil
• 1/2 tsp kosher salt
• 1/2 tsp sugar (optional, helps browning)
• 1 tbsp water or dry white wine, to deglaze (optional)

For the Sausage & Spinach

• 12 oz bulk breakfast sausage (mild or hot)
• 2 garlic cloves, minced
• 5 oz baby spinach
• Pinch red pepper flakes (optional)

For the Custard

• 10 large eggs
• 2 cups whole milk
• 1 cup half-and-half (or heavy cream for richer)
• 1 tbsp Dijon mustard
• 1 1/2 tsp kosher salt
• 1 tsp freshly ground black pepper
• 1/4 tsp ground nutmeg
• 2 tsp fresh thyme leaves (or 1/2 tsp dried thyme)

To Assemble

• 1 lb day-old crusty bread (sourdough or ciabatta), torn into 1 1/2-inch pieces (about 10 cups)
• 8 oz Gruyère cheese, shredded (about 2 cups)
• 1/2 cup finely grated Parmigiano-Reggiano
• 1 tbsp unsalted butter, for greasing the dish
• Chopped fresh chives or parsley, for serving

Step-by-Step Instructions

Step 1: Prep the pan and bread

Grease a 9×13-inch (3-quart) baking dish with 1 tbsp butter. Tear the day-old bread into 1 1/2-inch pieces. If your bread is very fresh and soft, dry it: spread on a sheet pan and bake at 300°F for 10–12 minutes until dry to the touch but not browned. Let cool while you prepare the fillings.

Step 2: Caramelize the onions

In a large skillet, heat 2 tbsp butter and 1 tbsp olive oil over medium-low. Add the sliced onions, 1/2 tsp kosher salt, and optional sugar. Cook, stirring occasionally, until deep golden and jammy, 25–30 minutes. If the pan looks dry or browned bits build up, splash in 1 tbsp water or wine to deglaze. Scrape onions into a bowl.

Step 3: Cook sausage and wilt the spinach

In the same skillet over medium heat, crumble in the sausage. Cook, stirring, until browned and cooked through, 5–7 minutes. Stir in the minced garlic (and red pepper flakes, if using) for 30 seconds. Add the spinach and cook just until wilted, 1–2 minutes. Drain off excess fat and any liquid; set aside to cool slightly.

Step 4: Whisk the custard

In a large bowl, whisk the eggs, whole milk, half-and-half, Dijon, 1 1/2 tsp kosher salt, 1 tsp black pepper, nutmeg, and thyme until smooth and well combined.

Step 5: Layer the strata

Spread half the bread in the prepared dish. Top with half the sausage-spinach mixture and half the caramelized onions. Sprinkle with half the Gruyère and half the Parmesan. Repeat with remaining bread, sausage-onion mixture, and cheeses.

Slowly pour the custard evenly over the entire dish, pausing to let it soak in. Press the top gently with your hands or a spatula to help the bread absorb the liquid. Cover tightly with plastic wrap or foil.

Step 6: Chill overnight

Refrigerate the strata for at least 8 hours and up to 24 hours so the bread fully hydrates. If convenient, press the top once more after an hour to redistribute custard.

Step 7: Bake until puffed and golden

When ready to bake, preheat the oven to 350°F (175°C). Uncover the dish and set it on the counter while the oven heats, 10–15 minutes. Bake on the middle rack until the top is deep golden, edges are crisp, and the center is set (an instant-read thermometer in the middle should read about 160°F), 45–55 minutes. If the top is browning too quickly, tent loosely with foil for the last 10–15 minutes.

Step 8: Rest, garnish, and serve

Let the strata rest for 10 minutes to set the custard. Sprinkle with chopped chives or parsley. Slice and serve warm.

Pro Tips

• Dry bread makes the best texture—if it’s soft, toast it briefly so the custard doesn’t turn soggy.
• Season generously. Bread absorbs salt; the custard should taste well-seasoned before baking.
• Press the assembled strata before and after chilling to ensure even soaking.
• For an extra-crispy top, broil 1–2 minutes at the end, watching closely.
• Let it rest 10 minutes after baking; this keeps slices neat and custard silky.

Variations

• Mushroom–Leek Vegetarian: Swap sausage for 16 oz sliced cremini mushrooms and 2 thinly sliced leeks sautéed in butter. Add a splash of sherry while cooking.
• Ham & Swiss: Replace sausage with 12 oz diced smoked ham. Use 8 oz Swiss instead of Gruyère; add 1 tsp grainy mustard.
• Mediterranean Spin: Add 1/2 cup chopped roasted red peppers and 1/3 cup pitted Kalamata olives; swap Gruyère for half feta, half mozzarella.

Storage & Make-Ahead

Assemble up to 24 hours in advance and keep covered in the refrigerator. Baked leftovers keep 3–4 days refrigerated; reheat covered at 300°F for 15–20 minutes or microwave single portions until warm. To freeze unbaked strata, wrap tightly and freeze up to 2 months; thaw overnight in the refrigerator, then bake 55–65 minutes. Baked leftovers can also be frozen in portions for up to 2 months; thaw and reheat gently.

Nutrition (per serving)

Approximate values: 630 calories; 34g protein; 36g carbohydrates; 38g fat; 2g fiber; 1170mg sodium. Values will vary based on specific brands and sausage used.