Best Sit-Down Restaurant Desserts
This isn't a formal sit-down restaurant experience at all, but if you simply want to share a great dessert with a bit of booze to cap a night nicely, and on the casual end, Sweet Revenge has some of the best cupcakes in the city, and serves wine/beer at the bar or in its cafe-like table area. I'd recommend the red velvet/prosecco pairing...
If price is no object, and you require wine/liquor, I'd say it is a toss up between Tailor or WD-50. Both are more on the avant side but extremely tasty! I think Tailor is marginally more romantic, especially if you get a nice booth. If you don't mind ordering at a bar/counter, I like Chikalicious (though not as romantic) or the Bar Room at the Modern.
The big problem is with restaurants who don't specialize in dessert or have a crowd that dines early -- I would hate for you to get the evil eye because you're not ordering a full meal.