First, air pop the popcorn. To do this, place a large heavy-bottomed pot over medium-high heat on the stove, and cover it with a lid. Heat the empty pot for 2 minutes. After two minutes, put a few drops of water in the pot to see If it sizzles. When it does, add ½ cup popcorn kernels and place the lid back on the pot.When you hear the kernels beginning to pop, carefully lift the pot and shake it, repeating every 5 seconds. It should take about 3 minutes for the kernels to pop.
Make sure to consistently shake the pot to prevent the popcorn from burning. When the popping slows down, remove the pot from the heat. Pour the popped corn into a large bowl and set aside.
Repeat with the other ½ cup of kernels.
When popcorn is finished popping, quickly look it over and pick out any un-popped kernels. **This is important - don’t skip this step! Set the bowl of popcorn aside.
In a large non-stick saucepan, melt butter over medium heat.
Stir in brown sugar, karo syrup, baking soda and vanilla extract into the melted butter.
Bring to a rolling boil over medium heat (it boils quickly), then immediately reduce the heat to low. Simmer the mixture undisturbed on low heat for 5 minutes. Do not stir it!
Quickly pour the caramel mixture over the popcorn and stir with a stirring spatula to coat the pieces. *You may have to do it in batches unless you have a big bowl!
Preheat the oven to 250℉. Line 2 baking sheets with parchment paper.
Pour caramel corn onto lined baking sheets. Bake for 10-15 minutes, then remove the pans from the oven. Stir the candy, return to the oven, and continue baking for 10 more minutes, or until the candied popcorn is no longer ‘gooey’.
Notes
Remember to remove unpopped kernels. Trust me, you won't enjoy biting into one of those!
To easily look for unpopped kernels, pour the popcorn into a colander. Use one with large enough holes for the kernels to fall through. If you don't have a colander that will work, you can use the holes on a grid-style cooling rack.
When the caramel syrup comes to a boil, immediately turn down the heat and bring it to a simmer.