Stir butter and sliced Milky Way bars in medium saucepan over low heat until smooth; using a wire wisk if necessary. Remove from heat and stir in sugar and vanilla. Add eggs one at a time beating well after each. Stir in flour blended with baking powder and salt. Spread into greased square dish, bake at 350F for 25 minutes. Cool and cut into squares, dust with powdered sugar if desired.