Grease a 9x13 baking dish with cooking spray.
Cube the bread into small 1-inch cubes, and layer with the pecans in the prepared baking dish.
In a large mixing bowl, mix together the diced apples, melted butter, sour cream, sugar, brown sugar, corn starch, cinnamon, nutmeg, and lemon juice.
Toss the apple mixture with the bread and pecans in the baking dish.
In a large mixing bowl, whisk together the eggs, milk, vanilla extract, and salt.
Pour the egg mixture over the bread cubes and pecans in the baking dish, making sure all of the bread is soaked with the egg mixture.
Cover and chill for a good 4 to 6 hours or overnight.
When you're ready to bake the casserole, remove it from the fridge, and preheat the oven to 350° F.
In a small mixing bowl, mix together the sliced butter, brown sugar, and cinnamon.
Crumble or clump the topping over the entire breakfast casserole.
Cover the baking dish with aluminum foil, and bake at 350° F for about 40 minutes. Then uncover and continue baking for an additional 15-20 minutes.
Once it's thoroughly cooked through, remove it from the oven and let it cool for just a few minutes.
Then slice and serve with powdered sugar and/or maple syrup.