neutral oil, like grapeseed (You can also use coconut oil -- if you do, I suggest using coconut oil in place of butter, as well.)
butter (or less, if you insist)
Generous pinch of salt
Pour oil into a heavy-bottomed (at least 3-quart) saucepan. Add 3 popcorn kernels, and turn the heat to medium-high.
Wait for all three kernels to pop. Add the rest of the kernels, cover, and remove pot from heat. Count to 30 -- it helps to count out loud. Very, very loud.
Return your pot to medium-high heat. Once the kernels begin to pop -- they should do so almost in unison, thanks to the wait time -- begin shaking the pan back and forth with the lid slightly ajar. Don't get so vigorous that the lid flies off, okay?
Once the popping slows -- 2 to 3 seconds between pops is fine -- turn off the heat and empty your popcorn into a large bowl. While your pan is still hot, slide your butter in there, and let it melt. Once it begins to brown, pour it over your popcorn, and toss with a wooden spoon or rubber spatula to combine. Sprinkle with a fat pinch of salt.