Ingredients
2 tablespoons unsalted butter, plus more for dish
1 bunch leeks (4 to 6), white and palegreen parts only, halved lengthwise, cut into 1/4-inch-thick half-moons, and rinsed well (about 3 heaping cups)
1 teaspoon coarse salt, plus more for seasoning
1/4 teaspoon freshly ground pepper, plus more for seasoning
8 large eggs
1 quart milk
8 slices challah or brioche (1/2 inch thick)
6 ounces thinly sliced ham
2 tablespoons thyme leaves
1 cup grated Gruyere cheese (4 ounces)
1 cup grated fontina cheese (4 ounces)
Preparation
Preheat oven to 325°. Butter a 9-by-13- inch casserole dish. Heat the butter in a medium skillet over medium heat. Cook leeks, covered, until softened, about 5 minutes. Season with salt and pepper, and transfer to a small bowl.
Whisk together eggs and milk. Whisk in the salt and pepper. Set batter aside.
Layer the bread, ham, reserved leeks, thyme, and cheeses shingle-style in the buttered dish. Pour batter over top; press gently so bread absorbs liquid.
Bake until puffed and golden brown (tent with foil if edges brown too much before center is set), about 1 hour.