The bracingly tart, more brightly colored, flimsier-fleshed cousins of the sweet cherry, sour cherries are best not eaten out of the carton but cooked and tempered with sugar. They are scooped up so quickly by infatuated bakers that if you didn't know to come early for them, you might never even know they existed. Like ramps or fava beans or peaches, their arrival marks a hyperspecific microseason—in their case, early summer—and one that a tribe of devotees waits for with pie plates at the ready. These loyalists mostly dwell in Michigan's Fruit Belt, which grows 75 percent of the country's supply, or in Utah, Washington, New York, Wisconsin, and Pennsylvania. As little as one late frost can wipe out most of a season's supply, and even the longest runs are over in a month at best.