Preheat oven to 350 degrees F. Using 1 tablespoon butter, generously grease a 9x13 inch casserole dish. Leave any extra butter in casserole dish.
Cut bread into 1-inch cubes and place cubed bread in an even layer in prepared baking dish. Set aside.
In a medium bowl whisk together milk, eggs, vanilla, maple syrup, and cinnamon. Pour French toast custard over bread in the casserole dish. (If not baking right away, cover dish and refrigerate. See note section above.)
Sprinkle streusel topping evenly over the bread mixture in the casserole dish.
Bake, uncovered, in a preheated 350 degree-F oven, for 30-40 minutes until golden and French toast is set.
Milk: Any milk will work in this recipe or you could use equal parts milk and half and half or cream.
Bread: I prefer the Texas toast style bread for this, but have used French bread, sourdough bread, whole wheat bread, leftover hot dog and hamburger buns and leftover croissants.
Inspired by several recipes including one from Diamond Nuts