Heat a large pot over medium-high heat and add oil. Add a few kernels. When popped, add the rest of the popcorn kernels and cook, covered, shaking the pan every 10-15 seconds until popcorn is popped.

Make the caramel mixture by combining butter, brown sugar, corn syrup, and salt in a large microwave-safe bowl. Cook the mixture in the microwave for 45 seconds, remove and stir. Put it back for 1 minute 30 seconds, remove and stir. Microwave the mixture one last time for 1 minute 30 seconds, then remove and stir. The mixture will be nice and bubbly. Add vanilla extract and baking soda. Stir until the mixture stops bubbling, then pour the hot caramel over the popcorn.

Mix the caramel and popcorn and lay on a baking sheet to cool. Sprinkle with sea salt while still warm.