Once upon a time, my sister lived in Oklahoma. I went to visit her once and she made me the yummiest caramel popcorn ever. Here's her recipe:
Mindy's Caramel Popcorn
4 bags plain microwave popcorn *
1 can sweetened condensed milk (small can)
2 cups brown sugar, firmly packed
1/2 cup butter (or margarine)
1 cup light corn syrup
pinch of salt
Pop all of the bags of popcorn and remove kernels (very important!). Separate into two large bowls. Set aside.
Spread out 3 or 4 large sheets of wax paper on your table or counter - this will be where the popcorn cools.
Combine the remaining ingredients in a large, heavy saucepan. Start it on medium heat, until the butter melts. Raise heat slowly and bring to a boil. Continue to stir so that it doesn't burn. Boil for 5-7 minutes, stirring constantly, until it reaches the soft-ball** stage. Pour hot caramel over popcorn in small batches. Stir to coat, and then add more caramel if you'd like. Spread onto wax paper and let cool. Store in large ziplock bags.
*I am never able to find plain microwave popcorn. I buy the "light" popcorn and it works fine. I also only use 3 bags of popcorn, since that's what usually comes in one box. It also makes the caramel-to-popcorn ratio higher.
**The soft-ball stage has nothing to do with sports. To do the soft-ball test, keep a small bowl of cold water next to the stove. Drop about one teaspoon of caramel into the water and use your fingers to make the caramel into a little ball. If it forms into a soft ball, then it's ready. If not, then boil another 2 minutes and test again. You will probably do several of these tests before you hit the soft-ball stage. Just be sure to use clean water for each test.