Step 1

Preheat the oven to 200°F (93°C). Spread the popcorn out onto 2 large baking sheets. Set aside.

Step 2

Combine the sugar, corn syrup, butter, cream of tartar, and salt in a medium saucepan over medium heat. Stir constantly as the butter melts and mixture comes to a boil. Boil, without stirring, for 4-5 minutes. (If you have a candy thermometer, the mixture should be 234°F-235°F (112-113°C). Remove from the heat and quickly stir in the baking soda. Caramel will be foamy and frothy. Pour the caramel over the popcorn and stir gently until all the kernels are coated.

Step 3

Bake for 1 hour, stirring every 20 minutes. Allow to cool on the pan and break apart large clusters if desired. Cover the popcorn tightly once cooled.