Beat butter and brown sugar till light and fluffy. Beat in vanilla and eggs
Stir in flour, blended digestive crumbs, baking powder, and salt.
Press half in a well greased 9x13" pan that has been lined with parchment paper or foil.
Spread the marshmallows all over the crust base. Sprinkle chocolate chips over the marshmallow layer.
Flatten pieces of the remaining dough between your hands and place them evenly over the chocolate. It's fine if some of the filling is showing. Add any leftover chocolate or marshmallows over the top.
Bake at 180° for 30-32 minutes. Allow to cool then slice and enjoy!
