Prepare a baking sheet by oiling with butter or lining with parchment. In a large pot, bring the water to a boil with the vanilla bean and simmer for one minute. Remove the vanilla bean (squeezing out any vanilla-y water from the inside) and add the vanilla seeds, sugar, corn syrup, and butter or oil to the pot. Turn the heat to medium-high and stir until the butter is melted and sugar is dissolved. Cook until the sugar is a dark amber color (about 320°F), being careful not to burn. Remove from heat and quickly stir in the salt and baking soda. Be careful because these additions will cause the caramel to bubble. Quickly add in the popped popcorn and stir quickly and carefully until the kernels are evenly coated. Pour the mixture onto the prepared baking sheet. If you like your caramel corn clumpy, let it cool, as is. For individual pieces, separate kernels with your spatula. After the mixture is cool to the touch, (be patient or you'll burn yourself - I know!), you can use your hands to keep breaking up the clumps. Store in an air-tight container.
Recipe by IronWhisk at http://www.ironwhisk.com/2012/02/caramel-popcorn/