Combine popcorn & nuts in a large bowl (one that will clean easily). Make sure to throw out any kernels that didn’t pop. Line two baking sheets with parchment paper, set aside.
Melt the butter then add sugar and corn syrup. Stir until the mixture boils. Turn down heat and continue cooking until it thickens and turns a nice caramel color (10-12 minutes), stir occasionally.
Remove the caramel mixture from heat and stir in the vanilla with a heat-proof spatula.
Pour the mixture into the bowl of popcorn & nuts, stirring vigorously until coated (like you would when making Rice Krispie treats but don’t use your bare hands – this stuff is hot!).
Spread the popcorn mixture onto your prepared baking sheets and generously sprinkle with salt.
Let the caramel harden before breaking into clumps. Store for up to a week in an airtight container.