In a large pot with a lid, heat the oil over medium heat. Add a few of the corn kernels. As soon as they start to pop, add the rest of the kernels and remove the pot from the heat for 30 seconds, so that all the kernels gently come to the same temperature.

Put the pot back on the heat with the lid on, but just partially off center, venting so that some of the steam can escape. (Too much steam can make the popcorn soggy.) Shake the pan as the popcorn pops so that it doesn't burn on the bottom. Once the popping slows down, transfer the popcorn to a large bowl.

Drizzle the butter over the popcorn, sprinkle with salt, and toss. Add the nutritional yeast flakes, if desired.