Preheat the oven to 350 degrees F. Grease
an 8-by-8-inch baking pan and line with aluminum foil.
together the butter and sugars in a large mixing bowl until light and fluffy. Beat in the vanilla and eggs
until fully incorporated.
Mix together the flour, graham cracker
crumbs, baking powder and salt in a separate mixing bowl. Slowly add the dry ingredients to the wet ingredients until combined. Divide the dough in half.
Press half of the dough
into the bottom of the prepared pan. Sprinkle the chocolate evenly over the dough. Top the chocolate with the marshmallow creme. Spread the marshmallow
creme in an even layer, using a rubber spatula
that has been sprayed with nonstick spray.
Roll out the remaining dough to an 8-by-8-inch square on wax or parchment paper, using a rolling pin
. Working carefully, place the dough on top of the marshmallow layer
Bake until the crust
is golden brown, 30 minutes. Completely cool before cutting into bars.