Lightly grease a 9 x 13-inch baking dish, set aside.
Spread bread cubes evenly in the prepared baking dish.
In a large bowl, whisk together eggs, milk, half and half, brown sugar, granulated sugar, vanilla, cinnamon and sea salt.
Pour mixture over bread pieces in the prepared baking dish. Cover tightly with plastic wrap and store in the refrigerator for several hours or overnight.
Add butter, brown sugar, flour, cinnamon and sea salt to a medium bowl. Use a fork, pastry cutter or your hands and cut in the ingredients to combine until the mixture resembles coarse crumbs.
Cover and store in the refrigerator overnight.
When you’re ready to bake the French toast, preheat oven to 350 degrees F.
Remove the French toast bake and crumb topping mixture from the refrigerator and evenly sprinkle streusel over the top.
Bake for 40-50 minutes, or until the French toast is set and the top is lightly golden brown.
Serve warm with butter and maple syrup.
