1Heat oven to 350°F. In 3-quart saucepan, melt 2 cups chocolate chips and the butter over low heat, stirring constantly; remove from heat. Stir in flour, sugar, vanilla, baking powder, salt and eggs. Spread batter in ungreased 13x9-inch pan.
2Bake 27 to 34 minutes or until center is set. Cool completely, about 1 hour.
3In medium bowl, mix frosting, 1 cup chocolate chips and the walnuts. Spread frosting mixture over brownies. For brownies, cut into 6 rows by 4 rows.