Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking dish with non-stick spray or butter.
Place the cubed French bread in the prepared baking dish, spreading it evenly.
In a large mixing bowl, whisk together the eggs, milk, heavy cream, sugar, vanilla extract, cinnamon, and salt until well combined.
Pour the egg mixture over the bread cubes, ensuring all pieces are saturated. Gently push down any bread pieces that are floating to ensure even soaking.
Drizzle the melted butter over the top of the casserole.
Cover the dish with plastic wrap and refrigerate for at least 30 minutes to allow the bread to soak up the mixture (you can also refrigerate it overnight for added convenience).
Remove the casserole from the refrigerator and let it sit at room temperature while the oven preheats.
Bake in the preheated oven for 45 minutes, or until the top is golden brown and a knife inserted in the center comes out clean.
Let the casserole cool slightly before serving. Optional: dust with powdered sugar or serve with maple syrup.