Place a large heavy pot or Dutch oven pot on medium heat to warm up. Pour in enough butter to cover the base of the pot in a thin layer. Add in 2 kernels, place the lid on, and listen for them to pop.
Once the two kernels have popped, add the rest of the popcorn. It should cover the bottom of the pot in a single layer. Replace the lid and listen for the popping to get really rapid, shift the lid over a little so that it has a small crack to let out some of the steam
While the popcorn is still hot, pour the rest of the butter over the popcorn and sprinkle on the salt. Toss to coat it all.