The Book of Schmaltz: A Love Song to a Forgotten Fat.

Michael and Donna Ruhlman ($7.99 for iPad)

For many gourmands of a certain age, mashed potatoes topped with a hefty spoonful of schmaltz, or a handful of gribenes folded into a piece of soft, white bread, is the definition of heaven on earth. But that would make for a very brief collection. This app contains not only the instructions for creating the magical goo (rendered chicken fat flavored with onion, for the uninitiated) and its crackling byproducts (the gribenes), but also a couple dozen traditional and contemporary recipes to warm the heart and clog the arteries. IPad de-greaser not included.

Ruhlman, whose previous books were strictly treif, but no less delicious (Charcuterie, Salumi ) partners here with his 76-year-old Jewish neighbor Lois Baron ( An audio interview with her is all too brief.) and his wife Donna, who provides the helpful, at times mandatory, step-by-step photography. Among the classic recipes there is, of course, chopped liver, as well as the gribenes-stuffed matzo ball and the mighty knish. But they pale beside the dish known as helzel, a recipe that Hannibal Lecter surely would have loved, involving a large kishke wrapped in a broad swath of chicken skin with the wings still attached.

Among the contemporary recipes, vichyssoise with gribenes and chives just seems like bad karma. Harder to argue with is the pate de fois gras, a smoother version of chopped liver blended through with Spanish onion and a bit of red wine, presumably Manischewitz. The e-book version will be published this September.