Preheat your oven to 350°F (175°C).
Grease a baking dish and place the cubed French bread in it.
In a mixing bowl, whisk together the eggs, milk, heavy cream, sugar, brown sugar, and vanilla extract.
Pour the egg mixture over the bread cubes, making sure all pieces are coated.
In another bowl, mix the flour, brown sugar, cinnamon, and salt. Cut in the butter until the mixture resembles coarse crumbs.
Sprinkle the topping mixture evenly over the bread and egg mixture.
Bake in the preheated oven for 45 minutes or until the top is golden brown and the casserole is set.
Let it cool for a few minutes before serving.