Line an 8” pan with parchment paper. In a 4 quart saucepan, melt the butter over medium heat. Stir in brown sugar, salt, and corn syrup. Add the sweetened condensed milk. Cook the mixture to 248°, stirring constantly.
When the caramel reaches 248°, remove the pan from the stove. Allow the bubbling to subside. Stir in vanilla.
Pour the caramel in the parchment lined pan. Allow the caramel several hours or overnight to firm.
Use a dough cutter to loosen the sides that are not lined with parchment. Lift the parchment out of the pan.
Cut the caramel using a buttered dough cutter. Keep the caramels from touching one another after they are cut or they will begin to stick together.