1For bars, melt butter and chocolate in large pan over low heat. Stir in sugar, eggs, vanilla, flour, baking powder and nuts and mix well. Spread into a greased and floured 9 x 13 inch baking pan.
For filling, beat cream cheese, butter and sugar in medium bowl. Add flour, egg and vanilla. Beat til smooth and fluffy. Stir in the nuts. Spread over the chocolate layer. Sprinkle with the chocolate chips. Bake at 350 for 25 to 30 minutes or til a wooden pick inserted in the center comes out clean.
2For topping, sprinkle marshmallow on the hot baked layer. Bake for 2 minutes longer. Mix butter, chocolate, cream cheese and milk in large pan over low heat. Cook til smooth, stirring to mix well. Add powdered sugar and vanilla and mix well. Pour over the marshmallows and swirl together with a spatula. Cool on wire rack and cut into bars. Makes two dozen.