Measure out a piece of foil that is 4" larger than the diameter of the inner pot and wide enough to be able to fold into a pouch. Tuck the ends under the lip of the inner pot and make multiple holes with a thin sharp object. I used the pointy end of my cake tester. You don't want the holes too big or the butter will just pour out in places.
Add the 3 tablespoon of oil to the inner pot and 1 unpopped corn kernel. Turn the Ninja Foodi on High Sear/Sauté and cover with a silicone or glass lid.
While you are waiting for the one kernel to pop, cut or spread your butter on the foil.
When you hear the kernel pop, add in the remaining unpopped kernels and the salt. Stir to combine.
Close up the foil packet and secure by tucking under the lip of the inner pot. Cover with silicone cover or glass lid. Leave the sear/sauté on high until to begin to hear the kernels rapidly popping (less than 1 second between pops), turn the heat down to medium/low. Insert a spatula or wooden spoon and stir the bottom to move the kernels around.
Once the popping has slowed down to about 1 pop every few seconds, turn the Ninja Foodi off and stir again. If there is any butter left in the foil, shake it over the popcorn and stir.
Instructions for making Kettle CornFollow the recipe for making buttery popcorn except: Mix 1-2 tablespoon of sugar with room temperature butter and spread butter mixture over the bottom of the foil after you have poked holes in it.