Step 1

Stack several pieces of Swiss chard on work surface. Remove stems and set aside. Roughly cut leaves into pieces about 2-inch square. Repeat with the remaining swiss chard. Transfer the chopped leaves to a salad spinner filled with water. Drain, repeat washing if necessary, and spin dry. Rinse and chop the Swiss chard stems (about the same size as the diced onion.)

Step 2

Heat oil in a large heavy skillet over medium high heat. Add chopped chard stems, garlic, onion, salt, thyme, nutmeg and pepper and cook, stirring often until the onions are starting to brown, 6 to 8 minutes. Add chopped cleaned Swiss chard leaves, 2 tablespoons water and cover. Let wilt, 2 to 4 minutes. Remove lid and continue cooking, stirring occasionally until the Swiss chard is completely wilted and softened, 1 to 3 minutes. Remove from the heat and drizzle with balsamic vinegar if using. Serve hot.