Generously butter a 13 x 9 x 2-inch pan and set aside.
In a microwave-safe bowl, melt 1 cup butter. Once the butter is melted add 2 ½ cups packed brown sugar, 1 cup light corn syrup, and 1 (14-oz) can sweetened condensed milk and mix well. Microwave on full power for 4-5 minutes.
Remove from microwave and stir. Continue microwaving for 4-5 minutes. Stir again and add 1 tsp vanilla.
Pour the caramel into the 13 x 9 x 2-inch buttered pan. Let them completely cool for 1-2 hours. Cut the caramel with a knife and wrap in wax paper. Keep refrigerated.