NYT Cooking: Based on a classic gâteau Breton, this buttery tart is filled with a fresh plum compote flavored with honey, rosemary and cinnamon instead of the usual puréed prunes. You can make the compote and dough a few days ahead, but this tart is best served within 24 hours of baking. After that, the center starts to turn mushy from the moisture released by the fruit. Serve it on its own, or with a dollo...