In a medium saucepan mix sugar, Karo syrup and butter over medium heat. Continue stirring until mixture comes to a “ploppy” boil. Time for 7 minutes, NOT stirring.
Then add condensed milk. Mix well and continue stirring over medium heat. When mixture comes to a “ploppy” boil again, time for 13 minutes, stirring constantly.
Take off heat and add vanilla. Mix well and pour into a well-buttered 8"x 8" glass pan.
Cool overnight at room temperature.
Cut into bite-sized squares and wrap with squares of parchment paper.