Caramel Popcorn

1 C. butter (2 sticks, 1/2 pound) 1 pound brown sugar 1 cup light Karo syrup 1 can sweetened condensed milk vanilla 2 C. unpopped popcorn Pop popcorn into 2 bowls or 1 large enough to be able to stir. Take out as many unpopped kernels as you can from the popped popcorn. Melt butter, stir in brown sugar. Add Karo syrup, and while heating slowly stir in sweetened condensed milk. Bring to boil, stirring all the while. Boil on medium heat for 10 minutes Add 1 tsp. vanilla and pour onto popped popcorn. Stir in. Continue stirring occasionally to break it up until cool.