Pop the popcorn kernels using your preferred method (stovetop with vegetable oil, air popper, or microwave). Transfer to a very large bowl.
While the popcorn is still warm, drizzle the truffle oil evenly over the top.
Add the Parmesan cheese, sea salt, and garlic powder. Toss everything together really well so the popcorn gets evenly coated.
Sprinkle with fresh parsley if using. Taste and adjust seasoning if needed – some like it extra salty!
Serve immediately in individual bowls or a large serving bowl. Pro tip: make this right before guests arrive so it's fresh and warm.