Grease a 9x13 inch baking dish with butter.
Cut the loaf of bread into 1-inch thick slices and arrange half of the slices in the bottom of the baking dish.
In a mixing bowl, whisk together the eggs, milk, heavy cream, granulated sugar, vanilla extract, and cinnamon until well combined.
Pour half of the egg mixture over the bread slices in the baking dish.
In another bowl, mix the diced apples with brown sugar and a sprinkle of cinnamon, then layer them over the egg-soaked bread.
Arrange the remaining bread slices on top and pour the remaining egg mixture over everything, ensuring all bread is well soaked.
Cover the baking dish tightly with plastic wrap or aluminum foil and refrigerate for at least 8 hours or overnight.
In the morning, preheat the oven to 350°F (175°C).
Remove the cover from the baking dish and bake in the preheated oven for 45-50 minutes, or until the top is golden brown and the center is set.
Let it cool for a few minutes before serving. Optionally, serve with maple syrup and powdered sugar on top.