Chicken and Celery Pot Stickers

Cut celery into 2-inch pieces. With food processor running, drop in celery and garlic and finely chop. Stop motor and add chicken, 1/2 tablespoon soy sauce, sesame oil, and 1/8 teaspoon each of salt and pepper. Pulse until just combined.
Put 2 wrappers on a dry surface, keeping remaining wrappers in package, and lightly brush edges with water. Mound a rounded teaspoon filling in center of each wrapper. Fold in half, into triangles or half-moons, and pinch edges tightly to seal. Make 18 more dumplings in same manner.
Chop enough celery leaves to measure 1 1/2 tablespoons and stir together with remaining 3 tablespoons soy sauce and vinegar.
Heat vegetable oil in a 12-inch nonstick skillet over medium-high heat until hot, then arrange dumplings, slightly overlapping, in a spiral pattern and fry until bottoms are pale golden, 2 to 3 minutes. Add water, tilting skillet to distribute, then cover tightly with lid and cook until liquid has evaporated and bottoms of dumplings are crisp and golden, 6 to 7 minutes. (Use a spatula to loosen and lift edges to check bottoms; replace lid and continue cooking if necessary, checking after 1 to 2 minutes.) Remove lid and invert a large plate with a rim over skillet. Holding plate and skillet tightly together, invert dumplings onto plate. Serve immediately, with dipping sauce.