In a bowl, beat sugar, eggs, vanilla and salt on medium speed for 1 minute. Add butter; beat until blended. Combine flour and cocoa. Gradually add to sugar mixture; mix well. Stir in walnuts. Transfer to a greased microwave-safe 8-in. square dish. Microwave, uncovered, on high for 3-4 minutes, rotating every 1 minute or until a moist area about 1-1/4 in. in diameter remains in the center (when touched, brownie will cling to your finger while area underneath will be almost dry). Cool on a wire rack. Cut into bars.