Sister Mabel's Caramel Corn

From some religious mag Mama B. used to get. It's not cookies, but the holidays in our household were usually more about candy anyway. I mean, sure, we'd do the shaped sugar cookies and Russian teacakes, but it was also the time of year for cream caramels, peanut brittle, anise candy, and caramel corn. This one seemed the most kid-helper-friendly of the bunch, if only because it looks pretty cool when you add the baking soda.

Sister Mabel's Caramel Corn

Make 6 quarts of popcorn (finished measurement)

Combine:
2 cups light brown sugar
1/2 cup light corn syrup
1/2 cup butter
1/2 cup margarine
1/4 teaspoon cream of tartar
1 teaspoon salt

Put in heavy pan and boil until candy thermometer reads 260°. Remove from heat, stir in 1 teaspoon of baking soda. The mixture will foam up. Pour foamed mixture over popped corn and stir well.
Bake at 200° for 1 hour, pulling out every 20 minutes to stir. Adding nuts or whatever is optional. It gets less sticky as it bakes, so if you want to make popcorn balls, form them first.