1Heavily butter a 9 by 13 cake pan. Set aside.In a large heavy bottomed pot, combine sugar, milk and cocoa. Cook over med heat till boiling. Using a candy thermometer cook till soft ball stage stirring constantly. Remove from heat and add in vanilla and butter stirring until it looses its shine. Pour into prepared cake pan and let cool completely. Cut into 1 to 1 1/2 pieces.