Preparation Steps

• Preheat the oven to 250°F (120°C). Line two large baking sheets with parchment paper or lightly grease them.
• Heat a large heavy-bottomed pot over medium heat. Add the vegetable oil and three popcorn kernels; cover. When the test kernels pop, add the remaining popcorn kernels, cover, and shake the pot occasionally until popping slows to 2 to 3 seconds between pops. Remove from heat and transfer popped corn to a very large mixing bowl, discarding any unpopped kernels.
• In a medium saucepan over medium heat, melt the butter. Stir in the brown sugar, corn syrup, and salt. Bring the mixture to a boil, stirring constantly. Once boiling, stop stirring and allow to boil uncovered for 4 minutes without stirring.
• After 4 minutes, remove the saucepan from heat. Carefully stir in the baking soda and vanilla; the mixture will bubble and lighten in color. Immediately pour the hot caramel evenly over the popped corn and peanuts (if using). Use a heatproof spatula to gently toss and coat the popcorn thoroughly.
• Divide the coated popcorn between the prepared baking sheets in an even layer. Bake in the preheated oven for 45 minutes, stirring and turning the popcorn every 15 minutes to ensure even coating and crisping.
• Remove the baking sheets from the oven and let the caramel corn cool completely on the pans. Break into clusters and transfer to an airtight container for storage.
• Store in an airtight container at room temperature for up to 1 week. For extra crispness, re-crisp in a 250°F oven for 5 to 10 minutes before serving.