12 C popped popcorn (about 1/2 - 2/3 c kernels)
2 C brown sugar
1/2 C white Karo syrup
1 t salt (if you are using salted microwave popcorn then omit salt here)
1 cup margarine
1 t baking soda
2 t vanilla
Pop popcorn and set aside. Place brown sugar, Karo syrup, salt, and butter in a microwave safe dish. Cut up the butter into chunks so it melts better. Microwave for 30 seconds. That should be enough to melt the butter at least half way. Stir it all to combine. Now microwave on high for 2 minutes. Take it out and stir. Microwave for 2 more minutes.
While the caramel is cooking, put the popcorn in a big bowl. Use one that is way bigger than you think you’ll need. Also, try to get any un-popped kernels out so you don’t break a tooth. When the caramel is done cooking, take out of microwave and add baking soda and vanilla. Sit back and watch it do cool things like bubble and foam.
Stir it well and then pour it over the popcorn.
Mix it up well with a big spoon. I usually spread it all out on a piece of foil and let it cool for a minute so it doesn’t get stuck in one big clump. The longer it sits out, the firmer it will get, but it won’t ever get crunchy-hard unless you bake it.