Preheat the oven to 350℉ degrees. Spray a 9"x13" baking dish with non-stick cooking spray.
Cut the bread slices into 1-inch cubes. Place the cubed bread into the prepared pan. Set aside.
Crack eggs into a large mixing bowl. Add salt and whisk together.
Add the brown sugar, milk, cinnamon, nutmeg, and vanilla to the egg mixture and whisk until combined.
Pour the custard mixture over the bread, pressing down to moisten and coat all the pieces.
Bake for 45-55 minutes, or until the top is somewhat puffed, golden brown and a knife inserted in the center comes out clean.
Sprinkle the top of the casserole with powdered sugar and serve with fresh fruit and maple syrup.
Notes
Storage and Freezing
If you're not baking immediately, cover with aluminum foil, and place in the fridge overnight to bake the next day. Bring to room temperature while the oven is preheating. I usually bake the casserole for closer to 55 minutes when it's been in the refrigerator overnight.Store leftovers in the refrigerator, in an airtight container, and serve within 3-4 days. Wrap individual servings in plastic wrap, then place in a freezer Ziploc bag for up to 2 months. Thaw servings in the refrigerator and reheat them in the microwave until heated through.
Pro Tip
When I make this recipe, I use whole milk because it's what we have on hand. However, I've also had great results with using heavy cream. If you are using heavy cream, pour ¾ cup heavy cream into a liquid measuring cup. Add enough water to reach the 1 ½ cup line. This is the equivalent of using whole milk. We do not recommend replacing the whole milk with the same amount of heavy cream. If you'd like to cut this recipe in half, use an 8" x 8" dish.