Mr. Hagemajer took over and redesigned Bar Prasowy. Today, it has the same low prices and foods it did before the protest. But it is sleek and hip. Eastern Bloc-era accessories dot a modern interior. Much of the produce comes from local farmers.

“I am fond of Polish cuisine, but it’s vanishing,” said Robert Witecki, its chef. “Too often, people go to fast food restaurants. No one else wants to keep the tradition alive.”

Mr. Hagemajer added, “We wanted to create a place that was modern, one with roots in Communism, but with a modern quality.”

Such yearnings are not unique to Poland. In fact, “Red nostalgia” has swept across the former Warsaw Pact countries. In what was East Germany, “ostalgie” — a portmanteau of the words for “east” and “nostalgia” — is alive and well in tourism, fashion and nightclubs. In Bulgaria, many women yearn for a time when they were compensated by the state for domestic work.

“It is a kind of longing for the kind of sociality that existed under socialism, a feeling that these places represented a less-divided Poland,” said Kristen R. Ghodsee, a professor of Russian and Eastern European studies at the University of Pennsylvania, who has written extensively on the subject.

Some this is pure performance: Many milk bar patrons born after 1989 come as historical voyeurs, hooked on a bygone aesthetic.

“They have a certain feel of coolness about them,” said Dr. Parasecoli of N.Y.U. “It’s the hipster projection of what the milk bar experience was. They can look at it with detachment and irony because they didn’t live through a time when the milk bar was a necessity.”