I am taken with Mike G's point regarding the lack of "undergroundness," defined as something more experimental or daring, in the current crop of underground dinners (or perhaps only in the current crop that are well-known enough to be publicized). I agree with that, and wish there were a venue for the kind of dinners he references (maybe XmarX gets closer? I don't know right now, but if I find out, I'll let you know).
That said, I attended a Rabbithole dinner on Saturday, and was very pleased by the dinner as a whole, and excited by some of the courses. It started out with a gin-based mojito-like beverage, with fresh herbs (pineapple mint + others). The theme was cheese, so every course had a cheese element (far better than the nightmare I had earlier in the day, where it was five courses of beef). Courses also had wine pairings - since I didn't take a menu, I only remember some of the wines.
The first course was a fiddlehead soup with a burrata puff and oven-dried tomatoes. In our group, we all liked the flavor of the soup, but disagreed on the texture. I thought that the puree still had some unpleasant asparagus-like fibrousness (I was in the minority). The fiddlehead perched atop the puff had a nice crunch and fresh taste. This was paired with a verdicchio - don't know what maker.
Second was mussels in a broth with pecorino and fennel (possibly other things as well). They were tasty but unremarkable.
Things really started looking up at the third course - a ricotta tortellini with green olive tapenade and guanciale dust. This, paired with a riesling, was delicious. It hit all the right notes with the salty and tart toppings and the creamy cheese and slightly sweet wine.
The fourth course was excellent. It was a nicely-cooked venison roulade with blue cheese (forgot the maker, sorry). It was served with a morel poutine (with a seriously giant stack of morels). It was paired with a Jumilla, which was most people's favorite pairing of the evening. While I thought it was delicious, I thought the polarizing dessert was even better.
Dessert was a black truffle sweet roll, a dessert cousin to the savory truffle roll Mike Voltaggio made on Top Chef for the pork challenge, and serves as part of the bread service at his restaurant. It was served with roasted strawberries and goat cheese? ice cream (the ice cream may have also had creme fraiche - sorry for the spotty recollection). The strawberry-ness of the strawberries didn't contribute a ton to the dish; they were more just a sweet and fruity foil for the savory truffle and ice cream. While at the time, I said that it could have been any fruit, I'm not sure in retrospect that that's true. I think the strawberries, with their more subtle flavor, did a better job than any stronger fruit would have.
It also paired excellently with the dessert wine. Unfortunately, due to some kitchen accident (a broken bottle, it was said), some people in my party didn't get the dessert wine, and were instead poured some of the riesling from earlier, and offered a beer or a gin drink. They turned down the extra drinks and found the riesling to be a decidedly poor pairing (as did I). This may have affected their enjoyment of the dessert.
Our dinner cost $100 a person, not including gratuity. They told us this on the phone (and confirmed when we were confused at the table), but the envelopes for payment said $85 minimum, and unfortunately, it seemed that everyone else at the table went with the $85+tip.
All in all, while it may not have been groundbreaking, the food and atmosphere was quite enjoyable, and fun to meet other people who seek out such experiences (the chances are better for good conversation than at a random communal table, where some people don't want to talk to their neighbors). LTH events, obviously, fill much the same niche - headed over to the events board to see what's on tap....