Preheat oven to 250°F. Prepare a baking sheet with parchment paper or a silicone baking mat.
In a large stockpot over medium-low heat, heat vegetable oil and popping corn. Cover with a lid and optional splatter screen. Cook until popping kernels slow down. Transfer popcorn to a large bowl, discard un-popped kernels.
In a double boiler over simmering water, melt butter. Add brown sugar and corn syrup, stirring to combine. Remove from heat. Mix in vanilla and baking soda. Sprinkle with course sea salt, give a quick but gentle stir to disperse sea salt. Immediately pour over popcorn. Toss to coat well. Spread caramel coated popcorn on prepared baking sheet. Bake for 30-45 minutes, tossing every 15 minutes. Remove from the oven when caramel darkens slightly to a light amber.
Break up popcorn as caramel hardens. Store in an airtight container.