While Budapest still has a sizable Jewish community, there exist only four kosher restaurants and just a single kosher pastry shop in the city. They're all within the old Jewish Quarter, near the Kazinczy Street Orthodox Synagogue. Carmel and Hanna are meat, Kosher Deli and Tel Aviv Café dairy restaurants. If you don't keep strictly kosher, you could also try these Jewish-style, but non-kosher restaurants.
Hanna is a glatt kosher meat restaurant in Budapest's old Jewish Quarter operated by the Hungarian Autonomous Orthodox Jewish Community. Since the restaurant is buried within the fortress-like edifice of the congregation, most locals have never encountered Hanna, even though the surrounding area is currently the center of Budapest's nightlife, teeming with cafés, bars, and restaurants.