Place oven to 350 degrees.
Place butter and cake mix in a large mixing bowl. Using a pastry blender or a fork, cut butter into cake mix until crumbly. Sprinkle crumbles evenly over bottom of 15x10 inch jelly roll pan and press to form a crust.
Sprinkle chocolate morsels and pecans or coconut evenly over crust. Pour sweetened condensed milk evenly over all. Bake in preheated oven for 18-25 minutes or until light golden brown. Cool completely and cut into bars. Makes 4-5 dozen bars. Enjoy!