Nothing beats the summer joy of a farmers' market, with obscenely ripe tomatoes and berries vying with just-washed, glistening greens for your eyes, mouth, and dollars. But what happens in winter? Turnips might not have quite the same allure, but advice maven Umbra Fisk says it's possible to eat locally all year long -- even in bitterly cold New Hampshire, where today's letter-writer lives and eats.