Combine sugar and cocoa in an ungreased 10-inch square glass dish. Cut up butter in 4 or 5 pieces and drop onto sugar mixture. Pour in milk. Do not stir. Microwave on High 2-3 minutes or until mixture is bubbly.
Remove from oven and stir. Thoroughly stir in nuts and vanilla so nuts are evenly distributed.
Spread fudge even in dish. Refrigerate 1 hour. Cut into 24 pieces.