Coat a 9×13-inch baking dish with cooking spray and set it aside.

Chop the loaf of sourdough bread into 1 to 2-inch chunks. Arrange the bread in an even layer in the prepared baking dish.

In a large bowl, whisk 8 large eggs, 1 1/2 cups whole milk plus 1 1/2 cups heavy cream, 1/2 cup packed light brown sugar, 1 tablespoon vanilla extract, 1 teaspoon ground cinnamon, 1/2 teaspoon of salt, and 1/4 teaspoon of the ground nutmeg until smooth and combined.

Pour the custard evenly over the bread, then press the bread down slightly into the custard. Cover with plastic wrap and refrigerate overnight. Or to bake right away, let sit for 1 hour at room temperature to give the bread time to absorb the custard.

In a medium bowl, combine 1/2 chopped nuts, 1/4 cup all-purpose flour, the remaining 1/4 cup packed light brown sugar, the remaining 1/4 teaspoon ground nutmeg, and the remaining 1/4 teaspoon salt.

Add the softened butter to the nut mixture, and pinch and squeeze to incorporate the butter into the mixture until it forms moist, small clumps. Cover the crumble topping with plastic wrap and refrigerate until ready to bake.

When ready to bake, arrange a rack in the middle of the oven and heat the oven to 350°F. Take the casserole out of the refrigerator, uncover it, and set it aside at room temperature for 30 minutes to take the chill off while the oven heats.

Sprinkle the crumble topping evenly over the casserole and bake until the casserole is puffed, golden brown, and set, 45 to 50 minutes.

Remove from the oven and cool for 5 minutes before serving. Top with warm maple syrup, powdered sugar, and fresh berries. Enjoy!