Michael Ruhlman admits that it takes a certain amount of chutzpah for a non-Jew to tackle a topic like schmaltz—the onion-scented rendered chicken fat that powers traditional Ashkenazi Jewish cuisine. But that is exactly what the food writer did in The Book of Schmaltz: A Love Song to a Forgotten Fat, a digital cookbook he published for the iPad last month with his wife, photographer Donna Turner Ruhlman.In his defense, Ruhlman is a longtime “fat advocate,” promoting its culinary (and even health) benefits to a society largely dominated by fat-phobia. He is also co-author of Charcuterie, a book that he describes as an unabashed “ode to animal fat and salt.” So, late last summer, when his neighbor Lois Baron announced she was leaving a party early to go render some schmaltz in advance of the High Holidays, he seized the opportunity to get to know this new-to-him tribal fat.In Baron’s kitchen, Ruhlman discovered a powerful truth that most people, including many Jews, have forgotten: Schmaltz is incredible—“unrivaled in flavor,” according to Ruhlman. Inspired, he set out to share his newfound passion for schmaltz with the wider world.From a recipe-developing perspective, Ruhlman’s outsider status ironically gave him a creative edge. Yes, The Book of Schmaltz includes familiar dishes like kishke, matzoh balls, and chopped liver. (Ruhlman consulted extensively with Baron while testing these recipes.) But the book’s 20 recipes elevate their subject beyond standard Ashkenazi repertoire and bring schmaltz down a less-worn path: turning brioche dough savory (“schmaltz makes fabulous brioche,” Ruhlman said), flavoring fluffy Parisienne gnocchi, or rendering extra-crispy roasted potatoes. The book’s digital features, like the step-by-step photographs and a video clip featuring Baron, make schmaltz accessible and appealing to Jewish and non-Jewish cooks alike.***The use of schmaltz in Jewish cuisine was born in the cold-weather climates of Northern and Eastern Europe. Far away from the sun-ripened olive oil of the Mediterranean, Ashkenazi Jews created dishes based on the limited ingredients available to them. According to Gil Marks’ The World of Jewish Cooking, the non-Jews in these regions “generally used lard for cooking,” a practice Jews replicated with kosher animal fat. Each winter they slaughtered fattened-up chickens (or geese in some countries), rendering the fat and crunchy bits of skin (called gribenes) with chopped onions into an unctuous, flavorful cooking oil—thick and satiny when cold, liquid at room temperature—that could be used all winter.And use it they did. They crisped potato latkes and blintzes; bolstered their chopped liver, potato kugel, and kasha varnishkes (buckwheat groats and noodles); used it to flavor cholent and goulash; and spooned it onto slices of hearty bread. The savory bits of onion thrown in or on top of countless Jewish dishes were almost certainly browned in bubbling schmaltz. Even after arriving in America, where other cooking oils were more readily available, Eastern European Jewish immigrants continued to rely on schmaltz as a delicious, grease-slicked bridge back to their former homes.As a result, schmaltz tugs hard on the strings of Jewish nostalgia. Consider my mother. An otherwise devoted healthy cook and fat-skeptic, she kept a cloudy glass jar of chicken fat in the fridge each Passover when I was growing up. She had long since cut out other childhood treats like ice cream sundaes and french fries from her diet. But each spring, she continued to, as she told me, “render the fat off the soup chickens with onion and a few pieces of skin for gribenes to sneak,” because her mother’s matzoh-ball soup just was not the same without it.Like my mother, there are other diehard schmaltzies who never gave up on their beloved fat. The 83-year-old Sammy’s Roumanian Steak House on Manhattan’s Lower East Side still plunks a syrup dispenser filled with schmaltz on every table to be used as a condiment. And the schmaltz-laden matzoh balls bobbing in the Second Avenue Deli’s chicken soup are the stuff of slurpable legend.And yet, during the second half of the 20th century, schmaltz suffered heavily under this country’s low-fat/no-fat regime. Along with lard, butter, and other animal-sourced fats, it was marginalized as a public health threat and replaced in kitchens by “heart-healthy,” plant-based fats like olive oil and margarine. Meanwhile, to a certain generation of assimilation-minded, America-embracing Jews, schmaltz was shunned as a totem of their parents’ and grandparents’ unforgivingly ethnic poverty cuisine. At a low point in Jewish delicatessen culture, many cooks yielded to customer pressure, subbing flavor-deficient vegetable oil into their chopped liver and kishke.More recently, Americans have once again begun to embrace traditional cooking methods and ingredients—including the use of animal fats. New scientific evidence has also shed light on fat’s surprising health benefits, when consumed in moderation. As Daniella Cheslow wrote in Tablet, schmaltz “has less trans fat than margarine and more omega-3 fatty acids than most vegetable oils.” As a result, schmaltz has begun to make its way back onto tables—both Jewish and, thanks to Ruhlman’s cookbook, likely soon otherwise.The shift toward schmaltz is not immediately discernible on supermarket shelves. According to Moshe Morrison, Fairway Market’s director of kosher foods, sales have not changed on the Empire brand rendered chicken fat they sell at each of the store’s 12 locations. But that does not mean people are not rendering and using schmaltz at home. “Like stock and mayonnaise, store-bought schmaltz just does not compare to the homemade version,” Ruhlman said.Schmaltz has definitely found a home in the nouveau Jewish delicatessens and restaurants cropping up around North America. In Toronto, Zane Caplansky adds it to matzoh balls, chicken soup, chopped liver, and knishes at his popular deli, Caplansky’s, which opened in 2008. He also fries the onions for his lox, egg, and onion breakfast platter in what he calls “the quintessential Jewish cooking medium.” He said, “We have used schmaltz from Day 1, and there is simply no substitute.”Noah Bernamoff of Mile End Delicatessen, which opened in Brooklyn in early 2010, is also a committed fan. “If I had to pick a single food or ingredient that embodies what we do at Mile End today … it’d have to be schmaltz,” Bernamoff writes in the introduction to the recently published Mile End Cookbook. “We make our own schmaltz every day, and we use it for everything—as a seasoning, as a cooking fat, even to enrich our baked goods. We use it instead of oil in our vinaigrette. What’s not to like about schmaltz?” Not surprisingly considering the sheer amount of savory fat going into its food, Mile End has quickly become one of New York City’s best-loved restaurants.Despite Ruhlman’s unbridled enthusiasm for rendered chicken fat—or Caplansky’s or Bernamoff’s, for that matter—it is unlikely that schmaltz will erode olive oil’s kitchen dominance anytime soon. But its star is rising. Because underneath the country’s residual fear of fat lies a primal craving for straight-up, umami-driven flavor. And whenever it strikes, schmaltz is there to answer the call with its time-tested sizzle.***Like this article? Sign up for our Daily Digest to get Tablet Magazine’s new content in your inbox each morning.Leah Koenig is the author of The Jewish Cookbook,Modern Jewish Cooking: Recipes & Customs for Today's Kitchen, and The Little Book of Jewish Appetizers.