Swiss Chard can be harvested while the leaves are young or after maturity when they are larger and have slightly tougher stems. Young leaves (smaller than 4 inches) can be eaten fresh in salads. Mature leaves may be chopped and sautéed. The “ribs” can be eaten like celery.
At any point in the growing cycle, snip leaves 2 inches above crowns to rejuvenate plants. New, succulent leaves soon will be ready to harvest.
Cut Swiss chard stems into very small pieces. Tear leaves into 2″ pieces and rinse well (you’ll want some water still clinging to the leaves).
Heat oil in a large skillet over medium-high. Add chard stems, shallots, and garlic and season with salt. Cook, stirring occasionally, until vegetables are starting to soften but haven’t taken on any color, about 2 minutes. Add chard leaves, season with salt, and cook, tossing occasionally, until leaves are tender and have released some liquid, about 3 minutes (stems will have a bit of crunch). Mix in vinegar; taste and season with more salt if needed.