Lemons, with their bright, cheerful appearance and light, citrusy flavor, seem to sing summertime: think lemonade, lemon sorbet, lemon-blueberry anything. This fruit is so versatile, however, and so complementary to cool (cucumber, cilantro) as warm (ginger, cardamom) flavors, that neglecting to capitalize of their tart, sweet nature in winter-time baking would be a shame. Every…