Add 1 tablespoon of oil to the inner pot along with 1-2 corn kernels. Turn the Ninja Foodi on high sear/sauté and cover with glass lid or silicone cover. Allow oil to heat up and when the corn kernels pop, add remaining corn kernels.
Continue to heat on high sear/sauté until the kernels are popping rapidly, then decrease the heat to medium-low. Using a wooden spoon or silicone spatula and carefully stir a few times to ensure that most kernels pop and don't burn. When popping has almost stopped, turn the Ninja Foodi off. Uncover and stir. Dump the popcorn into a large bowl and wipe out the pot. You should have about 8 cups of popcorn. Try and remove any unpopped kernels.
Add butter, brown sugar, and corn syrup to the inner pot and turn the heat on high sear/sauté. Stir frequently, with a wooden spoon (or silicone) until butter is melted and the mixture starts to boil. When it starts to boil, do not stir.
Allow the mixture to boil for about 6-7 minutes and when the temperature reaches 300°F/149°C, turn the Ninja Foodi off.
Add in the baking soda and stir. The mixture will bubble and rise up. Add vanilla extract and stir. Immediately dump in the popcorn. Stir with a wooden spoon to coat with the caramel mixture.
When well coated, remove caramel popcorn and cool it on a cooling rack. Break up any large clumps of popcorn. When completely cool, serve and enjoy!