Preheat oven to 225°F. Lightly spray a large roasting pan with vegetable cooking spray. You can also use 2 disposable aluminum pans if desired. Pour the popped popcorn into the roasting pan and set aside.
PRO TIP: Have all ingredients pre-measured and close by the stovetop.
Combine the butter, brown sugar, corn syrup and salt in a large saucepan set over medium-high heat. Once the butter is melted and the mixture comes to a boil, reduce the heat to medium-low and simmer for 3 full minutes.
Remove from the heat and quickly stir in the vanilla and baking soda. Add the peanuts to the mixture and quickly stir to coat. Pour the hot caramel mixture over the popcorn. Gently toss and stir to coat using a large spatula or wooden spoon.
Transfer the popcorn to the oven and bake for 1 and 1/2 hours (90 minutes) stirring gently every 15 minutes until the popcorn is no longer tacky, mostly dry and the caramel is set. Cool completely before storing.
Notes
If using microwave popcorn avoid using brands with heavy butter seasonings.
Unflavored, unsalted fresh popped popcorn is best in this recipe. I typically use Spanish peanuts with the skin on or cocktail peanuts for this recipe.
Nutritional information is calculated using an ingredient database and should be considered as an estimate. When multiple ingredient alternatives are given, the first listed is calculated for nutrition. Garnishes and optional ingredients are not included.