Bourbon Sugar: Preheat oven to 150° or as low as your oven will go. Using a small paring knife scrape the seeds from the vanilla into a small bowl. Stir in sugar and bourbon. Spread on a parchment-lined baking sheet and let dry out in oven overnight, leaving door slightly ajar. Mixture should feel like the original sugar again in the morning (meaning it’s back to it’s dry state).

Fudge:
Line an 8x8" baking dish with parchment paper, leaving a generous overhang on 2 sides; lightly coat with nonstick spray.

Heat chocolates in a heatproof bowl set over a saucepan of simmering water (do not let bowl touch water) on medium heat, stirring occasionally, until almost completely melted (just barely hot). Set aside.

Combine condensed milk, butter, bourbon, corn syrup and kosher salt in a small saucepan; scrape in vanilla seeds and add pod. Heat over medium heat until barely hot (same as the chocolate).

Remove the vanilla pod from the milk mixture.

Gently stir one quarter of milk mixture into chocolate with a rubber spatula. Add another quarter of milk mixture, stirring to incorporate (it might look broken and greasy; don't worry, it will come back together). Continue with remaining milk mixture in 2 additions, stirring vigorously until fudge is very shiny and almost elastic, about 5 minutes. Scrape into prepared pan and smooth top. Sprinkle with bourbon sugar and sea salt. Let cool, then cover and chill at least 4 hours.

Turn out fudge onto a cutting board and slice into rectangles, squares or triangles.