Begin by popping 10–12 cups of popcorn using an air popper or stovetop. Remove any unpopped kernels and transfer to a large mixing bowl.

In a medium saucepan, combine 1 cup of unsalted butter, 2 cups of brown sugar, 1 cup of light corn syrup, and a pinch of salt. Heat over medium until it boils, then simmer for 4-5 minutes until thickened.

Remove from heat and stir in 4 cups of mini marshmallows until melted. Add 1 teaspoon of vanilla extract and mix well.

Pour the caramel mixture over the popcorn and fold it in until well-coated.

Spread onto a parchment-lined baking sheet. Cool for at least an hour, or bake at 250°F (120°C) for 30 minutes for extra crunch.

Once cool, break into clusters and serve in bowls or package for sharing.