The tables at Macesz Huszar were packed on a recent snowy afternoon in Budapest. The two-month-old restaurant's hip clientele looked like the usual foodie elite, whipping out smartphones to photograph their meals. But it wasn't culinary innovation that was drawing the crowds; it was the humble matzo-ball soup. A Jewish (but not kosher) bistro, Macesz Huszar offers delicious proof of the renaissance of Hungary's once vibrant Jewish culture, which was nearly destroyed by the Holocaust and the communist era that followed. Yet as one table happily tucked into plates of goose-skin cracklings and an egg-and-duck-liver salad known as Jewish egg, the...