Spinach and Gruyère Breakfast Casserole

Updated Feb. 3, 2025

Recipe Overview

A savory, make-ahead breakfast casserole featuring crispy baguette, wilted spinach, and melted Gruyère, elevated by nutmeg and a hint of cayenne. Perfect for gatherings or lazy weekend mornings, it benefits from overnight chilling to enhance flavor and texture.

Time Breakdown

  • Prep Time: 10 minutes

  • Cook Time: 1 hour 40 minutes (includes bread toasting, leek sautéing, and final baking)

  • Chilling Time: 8 hours (or overnight)

  • Resting Time: 10 minutes (post-baking)

  • Total Time: ~10 hours (approximate, including chilling)

Ingredients

  • Bread Base: 8 ounces (227g) crusty baguette (or similar), cut into 1.5-inch cubes

  • Butter: 6 tablespoons (85g) unsalted butter, divided

  • Salt: 1 teaspoon kosher salt (e.g., Diamond Crystal); adjust to taste

  • Leeks: 2 leeks, trimmed, halved lengthwise, and thinly sliced into half-moons (white and light green parts only)

  • Spinach: 10 ounces (283g) fresh spinach, washed and chopped

  • Spices: ¼ teaspoon grated nutmeg, large pinch ground cayenne, 1 teaspoon lemon zest

  • Vermouth/White Wine: 2 tablespoons dry vermouth (or dry white wine, e.g., Sauvignon Blanc)

  • Eggs: 8 large eggs

  • Cream: 2 cups (473ml) half-and-half (or 1 cup whole milk + ½ cup heavy cream, for richness)

  • Pepper: ½ teaspoon freshly cracked black pepper

  • Cheeses: 4 ounces (113g) Gruyère, grated (2 cups); ¾ cup (75g) Parmesan, grated (plus extra for topping)

Preparation Steps

Step 1: Prep the Baking Dish & Bread

  • Preheat oven to 350°F (175°C). Lightly butter a 9×13-inch (23×33cm) baking dish or gratin dish to prevent sticking.

  • Bread Toasting: Spread baguette cubes on a rimmed baking sheet. Bake for 8–10 minutes until crisp (the bread will dry out slightly, creating a sturdy base). Transfer immediately to a large mixing bowl.

Step 2: Season the Bread with Butter

  • Melt 4 tablespoons of butter (keep the pan warm to avoid clumping). Toss the toasted bread cubes with the melted butter and a pinch of salt until evenly coated. This ensures the bread absorbs flavor and retains structure during baking.

Step 3: Sauté Leeks

  • In a large sauté pan, melt the remaining 2 tablespoons butter over medium-high heat. Add leeks and a pinch of salt. Sauté for 5 minutes until tender and lightly golden (avoid high heat to prevent browning). Leeks should be soft but not mushy.

Step 4: Cook Spinach Mixture

  • Add half the spinach to the pan. Sauté with nutmeg, cayenne, and lemon zest until wilted (2–4 minutes). Stir in the remaining spinach and another pinch of salt. Cook 5 more minutes until most moisture evaporates (this step is critical to prevent sogginess).

  • Deglaze with vermouth/wine, cooking 2–4 minutes until the pan is nearly dry. Taste and adjust salt if needed. Transfer the spinach mixture to a bowl to cool slightly (warm spinach will cook the eggs prematurely if added too hot).

Step 5: Combine All Components

  • In a medium bowl, whisk together eggs, half-and-half, pepper, and 1 teaspoon salt. The egg mixture acts as a binder and enriches the casserole.

  • Add the egg mixture to the bread cubes and toss until thoroughly coated. Fold in the cooled spinach, 1¾ cups Gruyère, and ½ cup Parmesan. Use your hands for best mixing (the warmth of your hands won’t disrupt the mixture).

Step 6: Refrigerate to Rest

  • Transfer the mixture to the prepared baking dish. Cover tightly with plastic wrap or foil and refrigerate for 8 hours (preferably overnight). This resting period allows the bread to fully absorb the liquid, ensuring a cohesive texture and deep flavor.

Step 7: Final Bake

  • Preheat Oven: When ready to bake, preheat oven to 350°F (175°C).

  • Top with Cheese: Uncover the casserole and sprinkle the remaining ¼ cup Gruyère and ¼ cup Parmesan over the top for a golden, cheesy crust.

  • Bake: Bake for 50–60 minutes until the center is set (no visible liquid in the middle) and the top is bubbly and lightly browned. The casserole will puff slightly during baking—this is normal.

  • Rest: Remove from oven and let rest for 10–20 minutes before serving. This allows the dish to firm up and distribute heat evenly.

Chef’s Tips & Variations

  • Chilling Insight: The refrigerator’s cold environment is critical for the casserole’s texture; preheat the oven only when ready to bake (not during chilling).

  • Wine Substitution: Replace vermouth with dry white wine or 1 tablespoon apple cider vinegar for acidity without alcohol.

  • Halving the Recipe: Use 4 eggs, reduce all ingredients by half, and bake in an 8×8-inch dish for 35–40 minutes.

  • Gluten-Free Option: Use certified gluten-free baguette or sourdough cubes; ensure all dry ingredients are gluten-free.

  • Serving Suggestions: Pair with fresh citrus slices (lemon or orange) and a glass of sparkling water for an elegant brunch experience.

Note: The casserole’s make-ahead nature makes it ideal for holiday brunches or lazy weekends. Its rich, savory profile balances the earthiness of spinach with the nutty, melted Gruyère.