When Laura Silver was growing up in New York, her family would drive out of their way to Brighton Beach, Brooklyn, to pick up Mrs. Stahl’s Knishes to bring to her grandmother’s when they visited. Her father also grew up on those same knishes, and even though Fannie Stahl, the namesake of the store, was long deceased, in her imagination, Silver saw her as another grandmotherlike figure.

Silver, who still lives in Brooklyn, continued to visit Mrs. Stahl’s well into adulthood. So you can imagine her dismay when she arrived one afternoon in 2005 to see it replaced by the grand opening flags of a new Subway sandwich franchise. The site of Mrs. Stahl’s Knishes for over 70 years — and more important to her, the purveyor of the potato pastry that played a huge role in her family — was now a ubiquitous chain selling turkey subs.

Silver could have bemoaned this loss, and in fact, she still does. But she also credits it with starting her on a path to become the world’s foremost knish scholar and champion.

Her new book, “Knish: In Search of the Jewish Soul Food,” is out this week, and she’ll be talking about it in two San Francisco appearances on May 21 and 22.

Unlike the bagel, which is sort of a poster child for Jewish food, the knish is humble and understated, Silver says, an underdog if you will. “It’s not sexy, it’s the antithesis of chicken cacciatore,” she said in a Skype interview. “Though cocktail knishes are prominent at festive events like bar mitzvahs, it’s easy to overlook it. It’s often seen as the sidekick to a hot dog, and up until now, it hasn’t been given its due. That’s why I am a champion of the knish.”

While researching the origins of the knish took her to France, Poland and Israel, San Francisco plays a starring role in her narrative. Two years ago, she learned that a granddaughter of the famous Mrs. Stahl lives here and has her grandmother’s original recipe.

Silver visited San Francisco in 2012 and met granddaughter Toby Engelberg, heard her stories and, of course, made knishes with her. (The famous recipe was published in J.: www.tinyurl.com/mrs-stahls-knishes.)

She now considers Engelberg like family.

New Yorkers may be aware of a knish still being marketed as Mrs. Stahl’s and sold in the five boroughs at specialty food shops. The rights were sold to an Italian pasta-maker in New Jersey and are still made according to the original recipe, but something has been lost, according to those in the know.

The pastry originates from the area of Eastern Europe known as the Pale of Settlement. Amazingly, on a “roots” trip to Poland with several relatives, Silver learned there was a village near Bialystok called Knyszyn, and, amazingly, Silver’s mother’s mother is from that village. The discovery caused Silver to say, “I’m a direct descendant of the knish.”

In Poland, she learned perhaps the most surprising discovery about the knish, that non-Jews offered them to mourners.

“Jews commonly eat round foods during shiva also, so that was an interesting overlap for dealing with loss,” she said.

Her book includes famous moments from knish history, like the fact that they were almost served to Eleanor Roosevelt, and a retrospective of knishes in pop culture, like a “Welcome Back, Kotter” episode in which Juan Epstein tries to quit smoking, and Mr. Kotter admits he also suffers from an addiction: to knishes.

She also uncovers the history of its use in comedy as a slang word for a certain female body part, with Jewish comedian Sarah Silverman being the most recent offender.

While Silver’s favorite knish is kasha, not potato, she does define herself as a bit of a purist. She knew all about the Bay Area’s “Knish King,” Ramni Levy, who is making such things as a curried beef knish dipped in white chocolate, as well as another company making chocolate and tofu knishes, saying, “This is really pushing the boundaries.”

But then she concluded, “If we’re on the cusp of a knish renaissance, which I believe we are, who am I to turn down these flavors? I leave it to the public to decide.”

Laura Silver will champion the knish at 6 p.m. May 21 at the San Francisco Public Library, 100 Larkin St., S.F. and at 6:30 p.m. May 22 at Omnivore Books, 3885 Cesar Chavez St., S.F. www.knishe.me

“Knish: In Search of the Jewish Soul Food” by Laura Silver (300 pages, Brandeis University Press, $24.95)