Make sure you book a day in advance, because this place is very popular.
Although they have more common menu items as well, Bock Bistro specialize in dishes made of parts of the animal usually not eaten by many - liver, tongue, cheek, neck, feet etc. But they prepare them excellently.
My wife started her dinner with salmon tartare with wasabi cucumber while I ordered beef tartare with grilled goat's cheese. Both dishes were excellent, my tartare was one of the best I have ever eaten (and I ate that a lot while working and staying in Paris for years).
Main courses: Roasted duck breast with cranberry sauce and fried finger noodles, and for me fried goose liver (foie gras) with a quince sauce and toasted brioche. Mine was not the healthiest of choices but tasted very nice, while my partner stated the duck was excellent.
We were stuffed after that, so no dessert.
But check your bill when you get it. I had a bottle of Hungarian Pinot Noir, but was charged the 40 % more expensive alternative on the wine list, while we drank the cheaper one - and realised this only later. You are also separately charged for bread and for butter.
The staff also add 10% service charge to the bill while this is not mentioned on the menu - and without asking.
As to the atmosphere - it is very nice - when we were there they had a Hungarian accordion player entertaining the guests, and at the end of the meal he joined 3 male guests at one of the tables, so we were treated to an alcohol-inebriated chorus of Hungarian songs.
All in all, a memorable evening, but more expensive than expected......