heat about 1/2 an inch of veg/neutral oil in a heavy-bottomed saucepan or pot. season with about 1 teaspoon of salt and about 1/4-1/2 teaspoon cayenne, depending on your heat tolerance.
add in popcorn kernels, just enough to cover the bottom of the pan - you don’t want the kernels to poke above the oil.
lid the pan and shake it gently over a medium-high flame. the popcorn should start popping in about 3-5 minutes. keep shaking the pan over the flame until there are 1-2 second lags between pops. turn off the heat and pour the popcorn into a bowl.
toss the popcorn with about half as many mixed nuts. while tossing, squeeze a lime over the popcorn/nuts. taste and add more salt, cayenne, lime, etc as needed.
Make the caramel sauce:
prepare a rimmed baking sheet with either a silicone mat or wax paper.
wipe out your pan and combine equal parts water and sugar (let’s say 3/4 cup of each) in the pan. heat over medium.
stir just until the sugar has dissolved, then stop stirring and just let the caramel cook. if you have a candy thermometer, you’re aiming for about 158ºF. if you don’t, you’re aiming to cook the caramel for about 10 minutes.
remove the caramel from the heat and stir in about 1/2 a teaspoon vanilla extract. you don’t have to, but it’s nice.
there are 2 ways to get the caramel on the popcorn/nuts: either fold the popcorn/nuts into the caramel, or spread the popcorn/nuts on the lined baking sheet and drizzle the caramel over it and then kind of mix it all together. either way will feel a little awkward the first few times you do it. however you get the caramel onto the popcorn, do it as quickly as possible and then pat the popcorn out into an even layer on the baking sheet to cool.
when cool, store the caramel corn in a tupperware for up to a week.