Heat oven to 350°F.
Line 8 inch pan with nonstick foil and then you can lift it out when cool
Beat butter and sugar in large bowl until fluffy.
Add egg and vanilla; beat well.
Stir in flour, graham cracker crumbs, baking powder and salt. Beat until blended.
Press half of dough into prepared pan.
Lay chocolate bars over dough.
Spread with marshmallow creme (Tip: wet your spreader/knife if too sticky).
Scatter bits of remaining dough over marshmallow; carefully press to form a layer.
Bake 35-40 minutes or until lightly browned.
Cool completely in pan on wire rack. Cut into BIG bars.