The whole-animal approach in vogue at so many restaurants is not without its challenges. What to do, for example, with all that beef tallow crowding the fridges at Italian joint Sauce (78 Rivington St., at Allen St.; 212-420-7700), where in-house butcher shop Tiberio Custom Meats currently processes two cows a week? Co-owner Frank Prisinzano could’ve challenged his kitchen to a Top Chef Masters: Season 4–style competition to use the stuff up, but instead he decided to make old-fashioned beef soap—yep, like the kind you shower with. Prisinzano combines the tallow with lye and essential oils (oregano-mint, lemon-thyme, or eucalyptus) and sells it for $6 per large bar and $3 to $4 for smaller ones. The long-lasting, mildly sudsy product cleanses without stripping natural oils, leaving skin soft.