This recipe is adapted from Sarah Copeland's forthcoming book, "Feast" (Chronicle Books).It's a little tricky to describe a drink as "addictive" without giving people the wrong idea (it can be spiked with a splash of gin if you like). But this sparkling, restorative cooler is just what we crave after the heavy foods of winter. Its allure and backbone come from sorrel, an herb renowned for its fresh, lemony sourness. The leaves also lend a high note to salads. And when sauteed in butter, they cook down into a flavorful puddle -- in other words, an instant sauce for seafood or poached eggs.