Overnight French Toast Casserole

granulated sugar

ground cinnamon

ground nutmeg

large eggs

milk ((anything but skim))

half and half

vanilla extract

(14.5 - 16 oz) loaf sourdough bread, such as La Brea, cut into 1-inch slices then slices cut into 1-inch cubes*

melted butter (, plus more butter for baking dish)

Powdered sugar ((about 1 tsp), for dusting top (optional))

Real maple syrup or pancake syrup (, for serving)

all-purpose flour

packed light brown sugar

ground cinnamon

salt

unsalted butter, cold and diced into small cubes