In a large pot, heat oil over medium-high heat. When the oil is hot, add the popcorn kernels, cover with the lid, and cook until all of the popcorn kernels are popped. Keep shaking the pot gently as the popcorn is made.
Skip the above if you have 10 cups of popped popcorn already made (microwave, air popped, or store-bought plain popcorn can be used)
Make sure to remove any unpopped popcorn kernels, and add the popcorn to a large bowl.
Preheat the oven to 250°F/120°C, and line a sheet pan with a silicone mat, parchment or foil.
In a medium saucepan, over medium heat, combine butter with brown sugar and corn syrup.
When the butter is melted, give it a stir to combine and bring to a simmer. Allow it to simmer for exactly 4 minutes WITHOUT stirring.
When the time is up, remove the caramel from the heat and immediately stir in salt, vanilla, and baking soda.
Pour the caramel over the popcorn, and stir with a spatula so it covers as much popcorn as possible.
Spread on the prepared sheet pan, and bake in the oven for 40 minutes flipping the caramel popcorn every 10 minutes. Then remove from the oven, separate any clumps and allow it to cool for 15 minutes or until the caramel hardens.