In a large heavy-bottomed stockpot or Dutch oven, melt the bacon fat over medium-high heat. When the fat starts to shimmer, add the popcorn kernels and stir to coat in the bacon fat. Cook, stirring continuously, for 1 minute, then cover the pot with a lid; you should hear the kernels start popping after 30 seconds to 1 minute. Cook, shaking the pot often to prevent the
kernels from burning, until the sound of the popping kernels slows down significantly, 3 to 4 minutes. Turn off the heat but keep the lid on until the popping stops completely.
Remove the lid, season liberally with salt, then cover the pot again and give it a few good shakes, preferably turning it completely over with the lid on to evenly distribute the salt. Serve in a large bowl. Sprinkle with bacon bits, if desired.