Preheat the oven to 350°F. Spray a 9x13 pan with cooking spray or grease with butter. Cut the challah bread into bite-sized pieces using a bread knife or by hand tearing.
1 loaf challah, sourdough, or brioche
In a large bowl, whisk together the eggs, milk, heavy cream, brown sugar, granulated sugar, molasses, vanilla extract, cinnamon, ginger, and nutmeg.
6 large eggs, 2 cups whole milk, ½ cup heavy cream, ¼ cup brown sugar, ½ cup granulated sugar, 2 teaspoons vanilla extract, 3 tablespoons molasses, 1 teaspoons ground cinnamon, 1 teaspoon ground ginger, ¼ teaspoon ground nutmeg
Add the pieces of bread to the french toast batter mixture in the large bowl and gently toss until all the pieces of bread are coated. Transfer to the prepared baking dish.
Prepare the crumble topping. In a food processor, pulse the flour, sugar, and butter together. Alternatively, you can use a pastry cutter or your fingers to break the butter into pea size pieces and mix with the flour and sugar. Sprinkle over the top of the prepared casserole.
¼ cup unsalted butter, ¼ cup granulated sugar, ¼ cup all purpose flour
Bake at 350°F for 45 to 50 minutes. The center will be just a touch jiggly and the edges should be golden brown. Serve warm.
While the french toast casserole bakes, prepare the glaze. Mix together confectioners sugar and heavy cream. Using a spoon, drizzle over the french toast casserole.
½ cup confectioners sugar, 2 to 4 tablespoons heavy cream