Prepare the Casserole: Spray a 9x13-inch baking dish with non-stick cooking spray. Tear the loaf of bread into bite-size 1-inch pieces (you should have about 10 to 12 cups) and place in the baking dish in an even layer.
In a large bowl, whisk together the heavy cream, whole milk, eggs, brown sugar, vanilla, cinnamon, and salt. Evenly pour over the bread pieces in the baking dish. Using the back of a spoon, gently press down on the bread so that it is all submerged in the custard. Cover with plastic wrap and refrigerate overnight.
Make the Topping: In a medium bowl, whisk together the flour, brown sugar, cinnamon and salt. Add the butter and, using a pastry blender, fork, or your fingertips, work the butter into the flour mixture until only pea-sized pieces remain. Toss in the chopped pecans. Cover and refrigerate until ready to use.
Bake the Casserole: Preheat oven to 350 degrees F. Remove the casserole from the refrigerator and allow to sit at room temperature while the oven preheats.
Sprinkle the topping evenly over the casserole.
Bake until golden brown and puffed, approximately 40 to 50 minutes (an instant-read thermometer should register at least 165 degrees F when inserted into the center). Allow to rest for 5 minutes before serving. Top with powdered sugar and maple syrup for a traditional French toast flavor!
Nutritional values are based on one serving