Grease a 9x13-inch baking dish and arrange bread slices in overlapping layers.
In a large bowl, whisk together eggs, milk, cream, granulated sugar, vanilla, cinnamon, and nutmeg until smooth.
Pour the egg mixture evenly over the bread, making sure to soak all pieces. Press down gently with a spatula.
Cover tightly with plastic wrap and refrigerate overnight (or at least 4 hours).
In the morning, preheat oven to 350°F. Remove plastic wrap from the baking dish.
In a small bowl, mix melted butter with brown sugar and drizzle evenly over the top of the French toast.
Bake uncovered for 40-45 minutes until golden brown and puffed. The center should be set and not jiggly. Let cool for 5 minutes, then slice and serve with warm maple syrup.