Croissant Breakfast Casserole With Ham and Gruyère

Ingredients

• 6 day-old croissants, torn (360 g)
• 1 tablespoon butter (14 g)
• 2 leeks, sliced (250 g)
• 1 1/2 cups cooked ham, diced (225 g)
• 2 cups Gruyère, divided (200 g)
• 10 large eggs (500 g)
• 1 cup whole milk (240 g)
• 1 cup half-and-half (240 g)
• 1 tablespoon Dijon (15 g)
• 1 teaspoon kosher salt (6 g)
• 1/2 teaspoon black pepper (1 g)
• 1/4 teaspoon nutmeg (1 g)
• 1 teaspoon fresh thyme, chopped (1 g)

Instructions

1. Prepare dish. Heat oven to 350°F with a center rack. Butter a 9-by-13-inch baking dish and set it on a rimmed sheet pan. Melt butter in a skillet over medium-low heat. Cook leeks with a pinch of salt until soft and glossy, about 7 minutes; cool slightly.
2. Layer croissants. Scatter half the torn croissants in the dish. Add ham, leeks, and 1 cup Gruyère, then top with remaining croissants. Keep pieces loose, with a few flaky edges facing upward.
3. Whisk custard. Whisk eggs until no separate white remains. Whisk in milk, half-and-half, Dijon, salt, pepper, nutmeg, and thyme. Pour evenly over the croissants, directing custard into dry corners and around the edges.
4. Soak filling. Press lower croissant pieces lightly with a spatula, leaving upper flakes exposed. Let stand 20 minutes at room temperature so the custard reaches the center without flattening the pastry.
5. Add cheese. Sprinkle remaining Gruyère across the surface, including the corners. Leave the cheese loosely scattered rather than forming a thick, continuous blanket, which helps browned patches develop among the exposed croissant ridges.
6. Bake and rest. Bake 40 to 45 minutes, until puffed, browned at the edges, and 160°F in the center. If top darkens early, tent loosely with foil. Rest 10 minutes before slicing twelve squares, allowing the custard to settle and portions to hold shape.

Notes

• A 9-by-13-inch ceramic or metal dish works well. Avoid very deep dishes, which can brown the top before the center sets.
• Use cooked ham. If swapping in sausage, brown, drain, and cool it before layering so excess fat does not loosen the custard.
• Fresh croissants work after tearing and drying uncovered on a sheet pan for 30 minutes; this helps them absorb custard without becoming uniformly soft.

Nutrition Facts