1. Heat oven to 350°F. Grease 13x9x2-inch baking pan.
2. Place chocolate and butter in large microwave-safe bowl. Microwave at MEDIUM (50%) 1-1/2 to 2 minutes or until chocolate is melted and mixture is smooth when stirred. Add sugar; stir with spoon until well blended. Add eggs and vanilla; mix well. Add flour and nuts, if desired; stir until well blended. Spread in prepared pan.
3. Bake 30 to 35 minutes or until wooden pick inserted in center comes out almost clean. Cool completely in pan on wire rack. Frost brownies, if desired. Cut into squares. Makes 24 to 36 brownies.
CHIPPY CHEWY BROWNIES: Prepare brownies as directed, stirring in 1 cup REESE'S Peanut Butter Chips with flour. Bake as directed.
CAKELIKE BROWNIES: Stir in 1/2 cup milk with eggs and vanilla. Increase flour to 1-1/2 cups. Bake as directed.
CREAM CHEESE BROWNIES: Prepare brownies as directed, using 4 eggs. Spread in prepared pan. Beat 8-oz. pkg. softened cream cheese, 1/3 cup sugar, 1 egg and 2 tablespoons flour. Soon mixture over brownie batter; swirl with knife to marble. Bake 35 to 40 minutes.
ROCKY ROAD BROWNIES: Prepare brownies as directed; bake 30 minutes. Immediately sprinkle with 2 cups miniature marshmallows, 1 cup HERSHEY'S SPECIAL DARK Chocolate Chips or HERSHEY'S Semi-Sweet Chocolate Chips and 1 cup chopped nuts over brownies. Bake another 3 minutes or until topping melts together.