Heat oven to 350 degrees Fahrenheit. Grease 13x9x2-inch baking pan. In large microwave-safe bowl, place butter. Microwave at HIGH (100%) 2 to 2-1/2 minutes or until melted. Stir in sugar and vanilla. Add eggs, one at a time, beating well with spoon after each addition. Add cocoa; beat until well blended. Add flour, baking powder and salt; beat well. Stir in nuts, if desired. Pour batter into prepared pan. Bake 30 to 35 minutes or until brownies begin to pull away from sides of pan. Cool completely in pan on wire rack. Cut into bars. About 36 brownies. Hershey's is a registered trademark of Hershey Foods Corporation. Recipe may be reprinted courtesy of the Hershey Kitchens.