In a small saucepan, melt the butter over low heat.
Remove the saucepan from the heat and stir in the dried basil, garlic salt, and grated Parmesan cheese until well combined.
Spread the popped popcorn evenly across a large baking sheet or place it in a very large bowl.
Slowly drizzle the melted pesto butter mixture over the popcorn, tossing continuously to ensure every kernel is evenly coated.
Serve immediately for the best taste and texture.
Pour the butter mixture in a slow, steady stream while continuously tossing the popcorn to ensure the most even coating without making it soggy.
Add a pinch of red pepper flakes along with the basil and garlic for a subtle, spicy kick.
