Add oil to a large pan and ensure it fully covers the bottom.
Add a few kernels to the pan and cover, on a low heat.
When one kernel pops, the oil is ready - add enough popcorn to cover the bottom of the pan.
Shake to cover everything evenly in oil and remove from heat for 30 seconds to warm up the kernels.
Return to a low heat, with the lid slightly ajar to prevent the popcorn going soggy.
Once the corn starts popping, reduce the heat and shake the pan occasionally to stop it burning.
Wait until all the corn has popped, remembering to shake the pan regularly.
Pour the popcorn into a large bowl, return pan to heat and add butter.
When the butter has metled, add the popcorn, shake, add salt, shake, and serve.