In a bowl, whisk together eggs, milk, heavy cream, sugar, and vanilla.
Arrange bread in an even layer in a greased 13"x9" pan or baking dish.
Pour the egg mixture evenly over the bread, and lightly press the bread down into the mixture.
For the topping, mix together flour, brown sugar, cinnamon, and salt in a bowl. Grate butter into the mixture, and mix until crumbly.
Cover both the baking dish and bowl. Refrigerate overnight.
Next day, remove both from the refrigerator while the oven preheats to 350°F. Evenly sprinkle the crumble mixture on top of the base. Bake 45-50 minutes or until the casserole is golden brown and set.
Serve with a variety of French toast toppings: maple syrup, fresh berries, whipped cream, chocolate drizzle, and sprinkles.
