Look for big, clean bulbs. Bright, feathery greenery at the top of the stalks (called fronds) are a sign of freshness. Keep fennel in a plastic bag in the refrigerator up to 5 days. Fennel is wonderful braised, roasted, grilled, sautéed, or raw. For a tangy salad: Toss 2 thinly sliced raw bulbs with 2 tablespoons each of lemon juice and olive oil, 1 ounce shaved Parmesan, and some salt and pepper.