Put the oil, popcorn and salt in a 6-quart metal mixing bowl. Cover with heavy-duty aluminum foil and poke 10 slits in the top with a knife.
Place the bowl over medium heat and shake constantly using tongs to hold the bowl. Continue shaking until the popcorn finishes popping, about 3 minutes.
Remove the bowl from the heat and carefully remove the foil. Stir in any salt that is on the side of the bowl.
Melt the butter in a microwave oven. Slowly drizzle it over the popcorn while spinning the bowl. Serve immediately.