Prepare a 9x13 baking dish with cooking spray or rub with butter.
Place croissant cubes in the bottom of pan.
Sprinkle cubes with pecan pieces.
In a large mixing bowl, combine milk and heavy cream. Whisk in both sugars, eggs, vanilla and cinnamon. Combine until smooth and well blended. Pour over the top of croissant cubes and pecans. Very gently press down cubes so they are all moist.
Cover with foil and refrigerate for 1-3 hours.
Preheat oven to 350°F.
Uncover and bake for 35-40 minutes. It should be nicely browned and slightly jiggly.
Let sit for 5-10 minutes as it will be very hot. Top each serving with vanilla ice cream or some type of warm caramel sauce.