Pop popcorn on the stovetop: Add the ¼ cup canola oil and add 3 individual popcorn kernels into a 6 quart saucepan. Cover and cook over medium-high heat until all three kernels have popped. Add the remaining kernels, cover, and remove from heat for 30 seconds. Then return the pot to heat and the kernels should begin popping within a minute. Cook, shaking occasionally until the popping sound slows, approximately 2 minutes. Near the end of popping, lift the lid slightly to let out steam and keep popcorn crisp.
Pop popcorn in air popper: add ½ cup popcorn kernels to the air popper and turn it on. Pop into a large bowl.
Pop in the microwave: Pop a bag of popcorn in the microwave according to bag instructions. Remove from microwave and open to allow steam to escape.
In a small omelette pan over the stove, add 3 Tbsp butter. Heat over medium high heat.
As butter begins to melt, add 1 Tbsp miso paste. Use a spatula to smear the paste into the butter and break up clumps as best as possible.
Cook for 1-2 minutes until the butter has a nutty aroma and bubbles. Cook for another 30 seconds after frothy bubbles.
Use a spoon or spatula to spoon some of the miso brown butter over the freshly popped popcorn. Sprinkle with kosher salt as desired. Repeat the process, tossing to evenly coat. Serve warm or store in an airtight container for up to a week.