Grease a 9x13 baking dish.
Arrange the brioche slices in the prepared baking dish.
In a large bowl, whisk together the eggs, milk, heavy cream, sugar, vanilla, cinnamon, and nutmeg.
Pour the egg mixture over the brioche, making sure all the bread is soaked.
Cover and refrigerate overnight.
Preheat oven to 350°F.
Bake for 45-55 minutes, until puffed and golden brown.
Serve warm.
