Line the cookie sheet with parchment paper so that all sides are overlapped with paper; crease paper to form to pan.
Line bottom of pan with a continuous layer of crackers
Place butter and brown sugar in saucepan. Over medium heat, melt, bring to a boil, and allow to gently bubble for 2 minutes, stirring continuously.
Pour mixture over crackers and spread to cover with spoon.
Bake at 350 F for 5 minutes.
Remove from oven and immediately sprinkle chocolate chips over surface.
Allow chips to melt for about 5 minutes and then spread with a spatula to cover.
Sprinkle with chopped nuts, crushed candy canes, sprinkles, MmMs, or any other topping that strikes your fancy.
Place in freezer for 20 minutes to set (make sure the pan is level).
Remove from freezer and remove from pan by holding the edges of the paper.
Place on cutting board. Allow to sit at room temperature for 5 minutes.
Cut into bars or squares!