1 cup butter or margarine, softened
1 1/2 cups sugar
2 teaspoons vanilla extract
2 2/3 cups all-purpose flour
1 1/2 cups graham cracker crumbs
2 teaspoons baking powder
1/2 teaspoon salt
8 1.5-ounce milk chocolate bars
2 cups marshmallow cream
Preheat oven to 350 degrees. Grease a 9-by-13-inch pan. In bowl, beat butter and sugar until light and fluffy. Add eggs and vanilla; beat well.
Stir together flour, graham cracker crumbs, baking powder and salt; add to butter mixture, beating until blended. Press half of dough in prepared pan. Arrange chocolate bars, breaking to fit as needed. Spread with marshmallow cream. Top with remaining dough, pressing to form a layer. Bake 30 to 35 minutes.