In a thin and shallow 3 1/2-quart pot, heat the oil over high heat. Put 2 kernels of popcorn into the pan, cover, and wait to hear them both pop. Remove the pan from the heat, take out the 2 popped kernels, add in the remaining kernels, cover, and let sit for 1 minute.Put the pot back over the stove on high heat. Within a few minutes, the popcorn should start popping. Give the pan a good shake every now and then to ensure even heating. Once the popping slows down to nearly a stop, remove the pan from the heat and let it sit for 1 more minute to give any stubborn kernels a chance to pop. Pour into a large serving bowl.Top with butter and salt if desired. Store any leftovers (ha!) in an airtight container in the refrigerator.