Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking dish with cooking spray or butter.
Cut the bread into 1-inch cubes and arrange them in the prepared baking dish.
In a medium bowl, whisk together the eggs, milk, sugar, vanilla extract, cinnamon, nutmeg, and salt until well combined.
Pour the egg mixture over the bread cubes, making sure each piece is coated well. Gently press down on the bread cubes to help them soak up the mixture.
Drizzle the melted butter over the top of the bread cubes.
Cover the dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 10-15 minutes, or until the French toast is golden brown and crispy on top.
Let the French toast cool for a few minutes, then dust with powdered sugar and serve with maple syrup.