Pop the popcorn according to the package instructions, typically using an air popper or stovetop over medium heat for about 3-5 minutes. Transfer the popcorn into a large bowl.

In a small saucepan, melt the butter over low heat until fully liquid and slightly bubbling, about 2-3 minutes. Remove from heat.

In a separate bowl, combine the melted butter, granulated sugar, vanilla extract, apple pie spice, and salt. Whisk until well mixed.

Slowly drizzle the butter and spice mixture over the popcorn, using a spatula to gently toss the popcorn until evenly coated.

Let it sit for about 5 minutes to cool slightly before serving. Optionally, spread it on a baking sheet lined with parchment paper.