For dough, combine flour, the 1/2 teaspoon salt, and 2/3 cup boiling water in a medium mixing bowl, stirring constantly with a fork. Add 1/4 cup cold water; mix with your hands until dough forms a ball. (The dough will be sticky.) Cover; set aside.
NOTE: I had to add a little bit more water than posted; go by the look and feel.
For filling, stir together hoisin and cornstrach in a medium mixing bowl. Stir in finely diced bok choy, carrot, finely sliced green onion, cilantro and salt. Add ground beef; mix well. Using about 1 tablespoon of the filling for each, shape filling into 30 balls. Set aside.
NOTE: I used an egg ring to form the wraps; made it easier for filling.
Divide dough in half. Return one portion to the bowl; cover and set aside. Divide the other portion into 15 balls. On a well-floured surface, roll each dough ball into a 3-inch circle. Place a meatball in the center of each circle. Fold the dough up and around all but the top of the meatball, pleating dough firmly. Gently flatten the bottom of each dumpling. Repeat with remaining dough and meatballs to make 30 dumplings total.
NOTE: Keep a moistened towel over the wontons so they do not dry out while you continue to make the batch.
Bring water to boiling in a steamer or Dutch oven. Place dumplings, open sides up, on a greased steamer rack; make sure the dumplings don't touch one another. (If all the dumplings won't fit on a steamer rack, refrigerate remainder until ready to steam.) Place rack over, but not touching, boiling water. Cover and steam dumplings for 16 to 18 minutes or until internal temperature reaches 160 degrees F. Meanwhile, combine rice vinegar and soy sauce. Sprinkle with 1 teaspoon thinly sliced green onion. Serve with dumplings.
NOTE: Used a rice steamer and oil sprayed the top insert each time.