Choose a pot large enough to hold the desired amount of popped popcorn. Popcorn has a volume expansion of over 25 times, so 1 tablespoon of kernels yields 1.5 cups of popped corn. (Measuring in milliliters? Here are some conversions.)
Coat the bottom of the pot with oil. Add two kernels to the pot, cover with a lid, and place over medium heat.
When the two kernels pop, turn off the heat and add the remaining kernels. Shake the pot so the kernels spread out evenly and let it sit for 1 minute.
Turn the heat back to medium. Leave the cover slightly ajar so steam can escape.
When it’s been 10 seconds since you heard the last pop, that was the last kernel!
What's going on?
Much of cooking is about managing heat transfer. When the first two kernels pop, the oil has reached a temperature high enough to boil the water inside the kernels and pressurize the pop. Adding the rest of the kernels slightly lowers the temperature of the oil, and letting them sit for a minute ensures they all get heated to just below the popping point. Without that minute of sitting, heating can be uneven, resulting in some early poppers, and some still heating up while the early ones burn. Warming the kernels yields a narrower range of popping times, leaving no kernel unpopped.