Preparation

• Prepare the Baking Dish: Spray a 13x9 glass pan with cooking spray, then evenly distribute the cubed brioche bread throughout the pan. Set it aside while you work on the custard.
• Mix the Custard: In a medium-sized bowl, whisk together brown sugar, cinnamon, nutmeg, and salt. Stir in the melted butter, then add the eggs, milk, heavy cream, and vanilla extract. Whisk until smooth without any visible egg yolks, and pour this heavenly mixture over the cubed bread.
• Toss the Bread: Gently toss the cubed bread using a rubber spatula or your hands to ensure most pieces are coated in the egg mixture. Be careful not to overmix, as you want to keep the bread intact.
• Refrigerate: Cover the 13x9 glass pan with plastic wrap and refrigerate overnight, or for a minimum of 3 hours. This allows the bread to soak up all those luscious flavors.
• Make the Crumble Topping: In a small bowl, combine the flour, brown sugar, oats, cinnamon, and salt. Add the cold, cubed butter and stir until coated. Use your hands to blend everything until the mixture becomes dough-like. Cover and refrigerate until you’re ready to bake.
• Preheat and Assemble: Preheat your oven to 350°F. Remove the casserole and topping from the refrigerator. Break up the crumble topping into small pieces and evenly spread it over the top of the casserole.
• Bake to Perfection: Place the casserole in the oven and bake for about 45-60 minutes, or until the crumble topping turns golden brown and crispy.