In medium saucepan, mix sugar, karo syrup and butter over medium heat. (Be sure the heat is not too high or the carmels will be hard). Continue stirring until the mixture comes to a "ploppy" boil. Time for seven minutes no stirring. Add condensed milk (off the heat) mix well, and continue stirring over medium heat. When the mixture comes to another "ploppy" boil again time for thirteen minutes, stirring constantly. Take off heat, add vanilla mix well and pour into a well-buttered 8 X 8 glass pan. Cool overnight or at room temperature for six to eight hours. Cut into bite-size squares and wrap in wax paper or parchment paper. Good luck.