Make-Ahead French Toast Casserole

Drying the Bread - Adjust oven rack to top third and lower third position and preheat oven to 250°F (120ºC). Set a wire rack inside two 13- by 18-inch rimmed baking sheets. Arrange bread slices in a single layer on racks and bake until bread is dried out, about 20 minutes, flipping bread and rotating baking sheets halfway through. Let cool 10 minutes.

Soaking the Bread - Meanwhile, butter a 9- by 13-inch glass or ceramic baking dish. In a large bowl, whisk eggs, vanilla, salt, nutmeg (if using), 1/2 cup of the sugar, and 1 1/2 teaspoons of the cinnamon to thoroughly combine. Add milk and whisk to blend. Working with 2 or 3 toasted bread slices at a time, soak bread slices in egg mixture, flipping once, just until the bread absorbs the liquid but remains intact, 1 to 2 minutes, then arrange bread in prepared baking dish, overlapping slices. Pour any remaining egg mixture over bread slices. Cover with plastic wrap and refrigerate until bread is saturated, at least 1 1/2 hours or up to 12 hours.

Baking and Broiling - Adjust oven rack to middle position and preheat oven to 325°F (160ºC). Let casserole sit at room temperature while oven preheats; remove plastic wrap. Bake in preheated oven until browned and set, about 40 minutes. Remove from oven and preheat broiler. Stir together remaining 1 1/2 teaspoons sugar and 1/4 teaspoon cinnamon in a small bowl. Using a pastry brush, evenly brush bread with melted butter, then sprinkle with cinnamon-sugar. Broil until bread is crisp and browned in spots, about 4 minutes. Serve warm with maple syrup, chopped nuts, powdered sugar, and fresh berries, if desired.