Pour popcorn in one bowl.

In a small bowl, combine cheese powder and ground mustard and mix thoroughly.

Drizzle with melted butter. Place second bowl over the top of the popcorn bowl creating a dome shape. Hold firmly and shake popcorn to distribute butter, flipping the dome a couple times.

Take the top bowl off and sprinkle with cheese mustard mixture. Place bowl back over the top and shake until all the popcorn is coated with the cheese.