Early last month, Ben Katchor and I sat in B&H Dairy, a narrow East Village restaurant, eating giant cheese blintzes topped with sour cream and discussing the finer points of their construction. Should they be rolled like an egg roll, or folded like a burrito? Deep-fried or pan-fried? Can you really make them with sliced white bread instead of the traditional pancakes? (Yes.)

Then I asked a deeper question: In what culinary universe does a dish of buttery pancakes folded around creamy fresh cheese need a garnish of sour cream?

Mr. Katchor shrugged. “It’s a dairy restaurant,” he said. “They go for it.”

Places like this, with menus of blintzes and borscht, onion rolls and matzo brei, all lavished with butter and cream, flourished in Lower Manhattan in the early 20th century.

The subjects of Mr. Katchor’s new book, “The Dairy Restaurant” (Schocken, $29.95), were community cornerstones: cheap, filling refuges that made it possible for Jewish immigrants in New York to eat out according to kosher laws, by keeping milk and meat strictly separated, with fish, eggs and vegetables as neutral go-betweens. Most of the restaurants in the book have been closed for years, but that has not ended Mr. Katchor’s devotion.