Spinach and Gruyère Breakfast Casserole By Melissa Clark Updated Dec. 19, 2023

Total Time 1 hour 50 minutes, plus at least 8 hours chilling and 10 minutes resting Prep Time 10 minutes Cook Time 1 hour 40 minutes, plus at least 8 hours chilling and 10 minutes resting

Like most of its kind, you can assemble the casserole the day before you want to bake it, then pop it in the oven an hour or so before serving. It will emerge puffed and golden on top, ready for its star-turn on any festive table.

INGREDIENTS

• 8 ounces baguette or other crusty bread, cut into 1 ½-inch cubes
• 6 tablespoons unsalted butter
• 1 teaspoon kosher salt (such as Diamond Crystal), more as needed
• 2 leeks, trimmed, halved and thinly sliced into half-moons
• 10 ounces fresh spinach
• ¼ teaspoon grated nutmeg
• Large pinch of ground cayenne
• 1 teaspoon finely grated lemon zest
• 2 tablespoons dry vermouth or white wine
• 8 large eggs
• 2 cups half-and-half (or use a mix of milk and heavy cream)
• ½ teaspoon freshly cracked black pepper
• 4 ounces Gruyère, grated (2 cups)
• ¾ cup grated Parmesan

PREPARATION

1. Step 1: Heat oven to 350 degrees. Lightly butter a 9-by-13-inch baking dish or a large gratin dish.
2. Step 2: Spread baguette cubes on a baking sheet. Bake until crisp, about 8 to 10 minutes. Transfer cubes to a large bowl and toss with 4 tablespoons melted butter and a pinch of salt.
3. Step 3: Meanwhile, in a large sauté pan, melt the remaining 2 tablespoons butter over medium-high heat. Add leeks and a pinch of salt, and sauté until tender and lightly golden, about 5 minutes.
4. Step 4: Stir in about half of the spinach leaves, a pinch of salt, nutmeg, cayenne and lemon zest, and stir until wilted, about 2 to 4 minutes. Stir in remaining spinach and another pinch of salt. Sauté until most of the liquid has evaporated, about 5 minutes longer. Stir in the vermouth and let cook for 2 to 4 minutes, or until the pan looks dry. Taste and add more salt if needed. Let spinach cool.
5. Step 5: In a medium bowl, whisk together eggs, half-and-half, pepper and 1 teaspoon salt. Add mixture to the baguette, tossing well. Add spinach, 1¾ cups Gruyère and ½ cup Parmesan, and toss everything until mixed (your hands work well for this).
6. Step 6: Pour mixture into prepared baking dish, cover, and refrigerate for 8 hours or overnight.
7. Step 7: When ready to bake, heat oven to 350 degrees. Uncover and top casserole with remaining ¼ cup grated Gruyère and ¼ cup grated Parmesan. Bake for 50 to 60 minutes, or until the center is set and no longer liquidy (it might puff, and that’s fine). Let sit for 10 to 20 minutes before serving.