First you need a large stockpot preferably one that has a heavy bottom. Pour your popcorn in the bottom just don't exceed a single layer of corn across the whole bottom of the pan. Add in oil enough to coat the whole bottom of the pan. And add about a 1/2 tsp of salt or so depending on how much corn you are popping. Then fire up your burner. When it starts to get really hot add in about 1/4 cup - 1/3 c sugar. Stir the sugar and kernels. Put on the lid before the corn starts to fly. Then every 5 seconds or so I pick up my pan and swirl it around. Then continue to let it pop. When the popping is really strong sometimes I pull the pan off the stove and continue swirling it and letting it cool off a touch. The risk that you run is from burning the sugar. Sometimes I pull off the lid and dump off the top and so I can continue to cook the kernels on the bottom.
This stuff is amazing. When it is done you should have white kettle corn. If it is a little bit brown then turn down your heat next time or spend more time pulling the pot off the stove. I have flat electric cooktop and I have tried this on gas too and the gas was a little more difficult. But you will not be sorry if you overcook a few batches until you get it perfect.
Good luck!
