In a medium saucepan combine sugar, syrup, and butter.
Cook, stirring constantly, over medium heat until sugar has dissolved and mixture comes to a full rolling boil. Allow to boil, without stirring, for exactly 1 minute; remove from heat and let stand for 5 minutes.
In another bowl or large measuring cup, combine evaporated milk, baking soda, and vanilla. Stir into the slightly cooled sauce.