Add the brown sugar and syrup and bring to a boil then turn down to a simmer and allow to cook for 5 minutes. Begin to stir every 30 seconds for another 4 minutes (up to 6 min depending on desired color.)
1 1/4 Cups Brown Sugar, 1/4 Cup Light Corn Syrup
Carefully add the vanilla, salt and baking soda while stirring. This will make it boil up so use a large pot and stand back.
Pour over the popcorn and stir until it is evenly coated.
10 Cups Popcorn
Spread the popcorn onto a nonstick prepared baking sheet in an even layer. Bake for 15 to 20 minutes, stirring every 5 minutes, until the caramel corn has turned a deep amber color. Remove the caramel corn from the oven and transfer to the counter lined with parchment or wax paper to cool. Store in an airtight container for up to 3 months.