Preheat the oven to 350°F.
In a large bowl, cream butter and sugar until well blended. Add eggs and vanilla; beat well.
In a separate bowl, stir together flour, graham cracker crumbs, baking powder and salt; add to butter mixture, beating until well blended.
Press half of dough in a prepared 9" x 13" pan. Reserve remaining dough. Bake 15 minutes.
After removing from oven, arrange mini or large chocolate bars over baked layer, breaking as needed to fit. Sprinkle with marshmallows; scatter bits of remaining dough over marshmallows, forming top layer.
Bake 10 to 15 more minutes or until lightly browned. Cool completely in pan on wire rack. Cut into bars.
HERSHEY’S® is a registered trademark of The Hershey Company.
Recipe is included with our Kitchen Essentials from Calphalon 9" x 13" Covered Cake Pan.