In a medium bowl, combine the flour, graham cracker crumbs, baking powder and salt. In a large bowl, using an electric mixer on medium speed, beat the butter and sugar until light, about 2 minutes. Beat in the eggs and vanilla until well combined. Reduce the mixer speed to low and add the flour mixture, mixing until combined. Divide the dough in half. Press half into the bottom of the prepared pan until the dough is evenly flattened. Dollop the marshmallow topping on top of the cookie base and gently spread into an even layer. Sprinkle the chocolate chips on top.

Scatter the remaining dough over the top in clumps. Don’t worry about completely covering the top, the marshmallow and chocolate chips should peek through. Bake the bars until golden brown, about 30-32 minutes. Cool completely. Remove the bars from the pan using the foil overhangs. Cut into bars and serve.