Beat butter and brown sugar till light and fluffy. Beat in vanilla and egg.
Stir in flour, crumbs, baking powder, and salt.
Press half in a well greased 9x13" pan that has been lined with parchment paper or foil.
Use the back of a wet spoon to spread the marshmallow creme over the crust.
Sprinkle chips over the marshmallow layer.
Flatten pieces of the remaining dough between your hands and place them evenly over the chocolate. It's totally fine if some of the filling is showing.