Position a rack in the center of the oven and preheat to 450ºSpread the cherries in a single layer in a small, rimmed baking dish or pan. Sprinkle with the sugar and 1 tablespoon of the bourbon. Roast the cherries in the oven, giving the pan a shuffle every 5 minutes, until they are oozing juice and beginning to collapse and look like prunes, about 15 minutes. Watch them closely so that the juices don't burn. Remove from the oven and let cool.
When the cherries are cool enough to handle, pit them (I did this with my fingers, breaking each cherry in half and removing the pit). Be sure to save all the precious juice. Chop the cherries coarsely - you want them in roughly quarters or eighths. (This can be messy, so wear an apron!) Combine the chopped cherries, their juice, and the remaining 2 tablespoons of bourbon in a jar and chill.
Make the vanilla bourbon ice cream base:
In a medium saucepan, warm the half and half with the vanilla bean pod and scrapings over medium heat until it steams and small bubbles form on the bottom of the pan, swirling occasionally. Remove from the heat, cover the pot, and let steep for 30-60 minutes.
Add the sugar and salt, and re-warm the half and half until steamy hot, swirling to dissolve the sugar.
Place the egg yolks in a medium bowl, and set the bowl on a damp towel. Place the heavy cream in a heatproof medium bowl and set a fine mesh strainer over the top.
Whisking constantly, dribble the hot half and half mixture into the egg yolks. Pour the mixture back into the pot and set it over a low flame. Stir the custard constantly with a heat-proof silicone spatula, scraping the bottom and corners of the pot well, until the custard thickens slightly and/or registers 170º on an instant-read thermometer. This will only take a few minutes.
Immediately strain the custard into the cold cream. Return the vanilla pod to the custard, and chill until very cold, at least 4 hours and (preferablovernight or up to 2 days.
Churn the ice cream:
Stir the bourbon into the cold ice cream base. Remove the vanilla pod (you can rinse it, let it air-dry, and stick it in a bottle of booze or a jar of sugar). Place the ice cream base in the freezer for 30 minutes to get it really cold, stirring once halfway through. Place the cherries in the freezer, too, along with a 9x5 metal loaf pan (or a vessel of equal size that will hold your finished ice cream).
Meanwhile, place the chopped chocolate in a heatproof bowl, and set the bowl over a pot of steaming (not simmerinwater, stirring occasionally until it is completely melted. Keep the chocolate warm.
Churn the ice cream base in your ice cream maker until it is the texture of a thick milkshake; it will take a little longer than usual due to the alcohol. Gently swirl in the chilled bourbon cherries and their liquid. I like to do this by hand with a spoon, so that the ice cream retains a marbled look of burgundy streaks on white, rather than becoming uniformly pink.
Finish the ice cream:
If the ice cream is soft and difficult to deal with, or if it becomes this way during the chocolate scribbling process, stick it in the freezer for 20 minutes or longer, until it's cold enough to behave itself.
Make sure your chocolate is warm and runny (but not hot). Working quickly to minimize ice cream meltage, spread about one quarter of the ice cream into the pan. Use a teaspoon to drizzle thin ribbons of about one quarter of the chocolate over the ice cream. Repeat with another layer of ice cream, then chocolate. Continue until you've used up all the ice cream, ending with a final layer of chocolate drizzle.
Place the ice cream in the freezer to harden; this will take about 4 hours or overnight. Once hardened, transfer the ice cream to an airtight container. It will keep for several months.