Spray your 9×13 baking dish with nonstick cooking spray.
Place your cubed bread in the baking dish.
Drain your sweet potatoes and mash well with a fork.
In a medium mixing bowl, whisk together the cream, sugars, eggs, sweet potatoes, vanilla, and pie spice.
Pour the egg mixture over the bread cubes pressing down to make sure all the bread got coated.
Cover with plastic wrap and refrigerate for at least 3 hours up to overnight.
Right before baking prepare the topping.
Combine the brown sugar, granulated sugar, butter, and flour in a small bowl.
I use my fingers to mix everything together until it is large coarse crumbs.
Sprinkle the topping all over the french toast casserole.
Sprinkle the pecans all over the top.
Bake in a preheated 350 degree oven for 50 minutes or until the casserole is no longer jiggly in the center. Let cool for a few minutes before serving. Serve with maple syrup, butter, and powdered sugar. Enjoy!