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.

For filling, stir together hoisin or soy sauce and cornstrach in a medium mixing bowl. Stir in bok choy, carrot, green onion, cilantro, and the 1/4 teaspoon salt. Add ground beef; mix well. Using about 1 tablespoon of the filling for each, shape filling into 30 balls. Set aside.

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.

Bring water to boiling in a steamer or Dutch oven. Place dumplings, open sides up, on a gresed 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 or white vinegar and soy sauce. Sprinkle with 1 teaspoon thinly sliced green onion. Serve with dumplings. Makes 30.