Heat the oil in a large pan with a tight-fitting lid. Once it is hot, drop in 3 corn kernels and put the lid on. When they pop, remove the pan from the heat, wait for 30 seconds, then tip in all the popcorn kernels, stir well, put the lid back on and put it back on the heat.
Now wait until all the popcorn has popped, shaking the pot occasionally, and holding th