Chocolate Chip Brownie Torte
["2/3 c. butter", "1 (12 oz.) pkg. semi-sweet chocolate, divided", "1 1/2 c. sugar", "1 1/2 c. all-purpose flour", "1 tsp. baking powder", "1/2 tsp. salt", "4 eggs", "1 tsp. vanilla extract", "1/2 c. chopped walnuts, optional", "Chocolate Chip Cream Frosting"]
["Preheat oven to 350\u00b0.", "Line jelly roll pan (15 1/2 x 10 1/2 x 1-inch) with waxed paper, grease.", "Heat butter and 1 cup semi-sweet chocolate in 3-quart saucepan over medium heat until melted.", "Stir remaining ingredients (except frosting) into melted chocolate. Spread evenly into pan.", "Bake 20 to 25 minutes.", "Cool 10 minutes. Invert on board.", "Remove wax paper.", "Cool completely."]
["butter", "semi-sweet chocolate", "sugar", "flour", "baking powder", "salt", "eggs", "vanilla extract", "walnuts", "Chocolate"]