Look for: Supple, deeply colored leaves without mushy spots.
Prep: Rinse thoroughly to remove sand; remove thick stems and shred leaves into 2-inch chunks. Rinse leaves again but do not dry.
Braise: Heat 2 teaspoons walnut oil (or canola oil) in a large skillet over medium heat. Add spinach or chard and toss until wilted. Add 1⁄2 cup dry white wine or dry vermouth. Cover, reduce heat and cook until wilted, about 5 minutes. Uncover and cook until liquid is reduced to a glaze. Sprinkle 2 teaspoons balsamic vinegar (or rice vinegar) over the greens.