1Heat oven to 350°F. Grease bottom and sides of 9-inch square pan with shortening. In 1-quart saucepan, melt baking chocolate and butter over low heat, stirring frequently; remove from heat. Cool slightly.
2In large bowl, beat sugar, vanilla and eggs with electric mixer on high speed 5 minutes. On low speed, beat in chocolate mixture. Beat in flour just until blended. Stir in nuts and chocolate chips. Spread in pan.
3Bake 40 to 45 minutes or just until brownies begin to pull away from sides of pan. Cool completely, about 2 hours. Spread with chocolate frosting. For regular brownies, cut into 6 rows by 4 rows; for mega-size brownies, cut into 3 rows by 3 rows.