Most of the ones I find are made with gram crackers I always used a chocolate cake mix.
Magic Cookie Bars - Cake Mix Version
Ingredients
1 (18 ounce) boxes chocolate cake mix
1/2 cup butter or 1/2 cup margarine, cold & cut into small pieces
1 cup chocolate chips
1 cup butterscotch chips
1 cup chopped nuts
1 cup flaked coconut
1 (14 ounce) cans sweetened condensed milk
Directions
Preheat oven to 325.
Place cake mix in a medium bowl, cut in the cold butter using a pastry blender. The mixture will remain crumbly.
Press mixture into an ungreased 10 X 15 pan.
Sprinkle chocolate chips, butterscotch chips, nuts, and coconut over the base.
Drizzle sweetened condensed milk over the whole pan.
Bake for 25-30 minutes, or until lightly browned.
Cool completely and cut into bars. (I like to cut them into large triangles).
Note: I have used other cake mix flavors for the base, such as yellow and butter, and they turned out well.