Combine sugar, molasses, corn syrup and milk in a heavy 3 quart saucepan.
over medium heat cook to 232°F Remove from heat and without stirring add butter (in thin slices) and vanilla. Let rest 1/2 hour or until cool enough to handle. Beat until fudge thickens and loses its gloss. Spread in 8x8-inch buttered pan. Cool and cut into squares.