In buttered 3-quart saucepan, bring first five ingredients to boil, stir constatnly. Boil without stirring to thread stage or until candy thermometer registers 234~F. Remove from heat. Add butter and vanilla. Do Not Stir. Cool to 110~F. Beat until fudge starts to loose its gloss, 10 minutes. Pour into buttered 8" square pan. Cool. Cut into squares. Makes 1-3/4 lbs.