Grease a 9x13-inch baking dish and spread half of the bread cubes evenly in the dish. Layer 1/2 the sliced peaches over the bread cubes. Top with the remaining bread cubes, then remaining peaches spreading them out evenly.
In a large bowl, whisk together the eggs, milk, heavy cream, granulated sugar, brown sugar, vanilla extract, cinnamon and salt until well combined. Pour the egg mixture evenly over the bread and peaches, ensuring all the bread is soaked. Drizzle the melted butter over the top.
Cover the dish with plastic wrap and refrigerate for at least 2 hours, or overnight for best results. *notes below if you don't have time for this
Preheat the oven to 350°F (175°C). Remove the plastic wrap and bake the casserole for 45 to 60 minutes, or until the top is golden brown and the center is set.
Allow the casserole to cool for about 10 minutes before serving. Dust with powdered sugar and serve with maple syrup or melted frosting on top if desired.
Notes
Tip: If you don't have time to let this rest in the fridge for several hours or overnight you should instead pour the cubed bread pieces into the bowl with the whisked egg mixture and very gently fold together. Then layer half in your pan, then layer 1/2 of peaches, then remaining egg bread and remaining peaches on the top. Drizzle melted butter on top and this can then be baked immediately.