Lightly butter the bottom and sides of a 9x13-inch baking pan. Shingle the sliced bread in the prepared baking pan (see photos).
In a large bowl, whisk the eggs. Add the eggnog, cream, milk, brown sugar, salt, cinnamon and nutmeg. Whisk until well combined. Pour the mixture evenly over the sliced bread. If necessary, flip the bread slices to soak up the liquids evenly.
Cover the baking pan with plastic wrap and let chill in the fridge for at least 3 hours (up to overnight).
Preheat the oven to 350 degrees F. Remove the plastic wrap and bake the casserole for 40 to 50 minutes until the bread is golden brown. Sift the powdered sugar over the warm French toast. Serve with maple syrup.
Notes
If using glass bakeware, allow dish to warm to room temperature before placing in the hot oven. Cold glass may shatter in the oven.
Nutritional information does not include powdered sugar and syrup.