Heat oven to 250 degrees F. Coat a large, deep roasting pan generously with nonstick cooking spray; set aside.Advertisement
Combine oil and popcorn in a large saucepan. Cover and cook over medium-high heat, shaking occasionally until kernels start to pop. Shake saucepan continuously until popping stops, then pour popcorn into prepared roasting pan.
Melt butter in a medium-size saucepan over low heat. Add brown sugar and corn syrup and bring to a boil over medium-high heat. Boil gently without stirring for 5 minutes or until mixture reaches 260 degrees F on a candy thermometer. Remove from heat and quickly stir in peanuts, vanilla and baking soda until smooth.
Pour corn syrup mixture over popcorn and toss to coat evenly. Bake popcorn at 250 degrees F for 1 hour, stirring every 15 minutes. Remove from oven and cool completely. Break up into small clusters and store in small canisters.