Grease a 9x13-inch baking dish and arrange your cubed bread evenly across the bottom. The pieces should fit snugly but not be packed too tightly—you want the custard to flow between every crevice.

Whisk together eggs, milk, cream, maple syrup, vanilla, cinnamon, and salt until completely smooth. Pour this custard evenly over the bread, making sure every piece gets coated. Press down gently with a spatula so the bread begins absorbing the mixture immediately.

Cover the dish with plastic wrap and refrigerate for at least 2 hours, or preferably overnight. This resting period is crucial—the bread transforms from dry cubes into custardy perfection.

Combine cold butter cubes, brown sugar, flour, and cinnamon in a bowl. Use your fingers or a pastry cutter to work the butter until the mixture resembles coarse crumbs with some pea-sized butter pieces.

Preheat your oven to 350°F. Remove the casserole from the fridge 30 minutes before baking. Sprinkle the crumb topping evenly across the surface.

Bake for 45-50 minutes until the center is set and the top is golden brown. A knife inserted in the center should come out mostly clean with just a few moist crumbs.

Let the French toast casserole rest for 10 minutes before serving. This brief cooling allows the custard to firm up slightly, making it easier to cut clean squares.