In a small saucepan, combine the butter and curry powder and cook over low heat, stirring frequently, until the butter has completely melted, about 2 minutes. Turn off the heat and set aside.
In a large heavy-bottomed stockpot or Dutch oven, heat the canola oil over medium-high heat. When the oil starts to shimmer (this should take about 3 minutes), add the popcorn kernels and stir to coat in the oil. 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 and drizzle the curry butter over the popcorn, then season with the salt. Put the lid back on (wipe it off first if it’s wet with condensation) and give the pot a few good shakes so the popcorn gets evenly coated with the butter and salt. Serve in a large bowl.