1 cup butter (2 sticks)
2 cups brown sugar
1 cup Karo syrup
1 can sweetened condensed milk
Bring first three ingredients to a boil, then add can of milk. Stir constantly. When it reaches a soft-ball stage, add 1 tsp. vanilla and remove from heat.
Pour over popcorn. Note to self: I think today I made 4 batches of popcorn, and it made enough caramel for one large bowl and large square tupperware perfectly.