Whisk Sugar, vanilla, and egg yolks together until they become pale and fluffy like a Bearnaise sauce.
Heat the cream until it comes to a simmer. Whisk in the chocolate until it melts evenly. remove from the heat.
Add the Hot liquid to the eggs, whisking constantly, one ladle at a time. The Heat of the cream will cook the eggs, so keep it moving so the eggs don't scramble. Add in the booze at this time.
Col the mixture by placing the mixing bowl into a larger mixing bowl filled with ice. Stir and whisk until it is completely cold. For best results, once cool, put in a fridge or freezer before moving to the ice cream maker. The colder it is to start, the better it will work.
Once properly chilled, Transfer to the bowl of an ice cream maker. Follow manufacturer's instructions to churn the custard. When done, transfer the frozen custard to a plastic or metal container, and put it in the freezer. It should set up enough to scoop within a couple hours.