Spray a baking sheet with non stick cooking spray, then put a layer of parchment paper in the baking sheet and spray that too to get it to stick.
Preheat the over to 250 degrees F (112 degrees C). Pop the popcorn and pour the popped popcorn and peanuts into two bowls.
Melt the (4 oz) stick of butter in a saucepan over medium heat. When it's melted, add the brown sugar, corn syrup and vanilla extract and bring to 250 degrees F (use a candy thermometer to watch the heat).
This next step needs to happen very quickly before the syrup hardens. Once the brown sugar syrup has reached 250, pour half over the popcorn in one bowl and put the rest of the syrup back on the stove. Mix quickly before the syrup cools and hardens, then pour the rest of the syrup over the second bowl of popcorn and mix quickly.
When thoroughly mixed, pour the popcorn mix onto the baking sheet you prepped earlier. It should be cool enough to handle by hand, so gently shape it to distribute the sticky kernels evenly across the sheet.
Put the sheet in the preheated oven and bake for an hour.