1. Heat oven to 350°F. Grease 8-inch square baking pan.
2. Combine butter, sugar and vanilla in medium bowl. Add eggs; beat well with spoon. Stir together flour, cocoa, baking powder and salt; gradually add to egg mixture, beating until well blended. Stir in chocolate chips and nuts, if desired. Spread batter evenly in prepared pan.
3. Bake 40 to 45 minutes or until brownies begin to pull away from sides of pan. Cool completely in pan on wire rack. Cut into bars. Makes 16 brownies.