Preheat oven to 325°F and line a 9×13″ baking dish with foil. Spray with nonstick spray.
Combine melted butter and graham cracker crumbs into a small bowl with a fork. Then press down crust in baking dish on top of foil.
Cream butter and sugar in a large bowl. Add in eggs and vanilla and stir until combined. In a separate bowl, mix the baking powder and salt with 1 cup of flour. Pour flour mixture into the butter mixture and stir in the rest of the flour. Fold in chocolate chips and marshmallows.
Press dough into pan with a spatula or flour on your hands. The dough goes right on top of the crust. Then add the candy bar pieces, graham cracker pieces and marshmallows on top.
Bake for 30-35 minutes, or until lightly browned. Oven temps will vary. Test with a tooth pick. The dough should be soft in the center.
Allow bars to cool and then enjoy with a scoop of ice cream or cold glass of milk!