Grease a 9×13 inch baking dish. Arrange the cubed bread evenly in the prepared dish.
In a large bowl, whisk together the eggs, milk, heavy cream, brown sugar, granulated sugar, vanilla extract, 1 teaspoon cinnamon, nutmeg, and salt until fully combined. This is your custard.
Pour the custard evenly over the bread cubes, pressing down gently to help the bread absorb the liquid.
In a small bowl, mix the 1/2 cup sugar and 2 tablespoons cinnamon for the swirl.
In a separate small bowl, mix the melted butter with the cinnamon-sugar mixture until it forms a thick, wet sand consistency.
Sprinkle this cinnamon-sugar mixture evenly over the top of the soaked bread.
Cover the dish tightly with plastic wrap. Refrigerate for at least 8 hours or overnight.
When ready to bake, preheat your oven to 350 degrees Fahrenheit (175 degrees Celsius). Remove the plastic wrap.
Bake for 45 to 55 minutes, or until the center is set and the top is golden brown. If the top browns too quickly, loosely cover it with foil for the last 15 minutes.
Let the bake cool for 10 minutes before serving.
Whisk together the powdered sugar and 2 tablespoons of milk to create a simple glaze. Drizzle over the warm bake before serving.
Notes
Brioche or challah bread works best because their richness prevents the bottom layer from becoming too soggy.
For a thicker glaze, reduce the milk to 1 tablespoon.
You can reheat leftovers covered in the oven at 325 degrees Fahrenheit for about 15 minutes.