Grease a 13" x 9" baking pan with butter.
Slice the bread into 20 one inch thick slices. Arrange the slices in the baking dish, overlapping slices to form two layers.
Mix the eggs, milk, half and half, sugar, vanilla extract, nutmeg, cinnamon and salt in a large bowl. Using a whisk or electric mixer beat the mixture well, stopping when bubbles form.
Pour the egg mixture over the bread, making sure the liquid reaches the lower layers of bread.
Cover and refrigerate overnight.
The next morning, preheat oven to 350 degrees.
Bake for 45 minutes.
Serve with maple syrup or powdered sugar, if desired, and enjoy!