Place enough oil into a large heavy based saucepan so that it just covers the bottom. Begin to heat the pan on a medium heat and add the popping corn. Next cover the pan with a tight fitting lid, when the popping starts shake the whole thing vigorously.
Once the popping has stopped remove the saucepan from the heat and allow it to cool for a few minutes, this allows any unpopped kernels time to pop.

Melt the butter in a microwave or pan, then gently pour over the freshly popped corn. Stir the popcorn until it is completely coated in the butter, then add salt to taste.