Measure Flour into a large mixing bowl; add boiling water, stirring quickly with chopsticks or fork, then add cold water and mix well. Work dough until smooth and supple. Roll dough into shape of a ball. Cover well with plastic wrap or damp cloth; set aside to rest for 1 hour at room temperature. Place the chicken in a small bowl; add cornstarch, cooking sherry and pinch of salt. Set aside and refrigerate and let marinate until ready to use. Stir-fry Chinese sausage and dried shrimp in hot vegetable oil in a small frying pan over high heat for 1 minute. Add chicken with its marinade and stir-fry for another 2 minutes. Quickly stir in barbecued pork and 3/4 cup of the minced onions. (Set aside remaining onions for pancake wrappers.) Immediately season with the oyster sauce, soy sauce, sugar and salt, and mix well. Turn off heat; divide into 16 portions and set aside. Knead dough until smooth and divide equally into 16 pieces; cover with plastic wrap. Work 1 piece of dough at a time, keeping the rest covered in plastic wrap. Take a piece of dough and rub both sides with a bit of shortening, then roll out with a rolling pin to 6 inches in diameter. Again rub shortening (about 1 teaspoon) onto 1 side of the dough; sprinkle evenly with about 1 teaspoon minced scallions and a pinch of salt. Curl up the dough from 1 end into a long, narrow cylinder; then curl up again lengthwise into a snail-like cylinder. Place the dough on its broad side and roll out again with a rolling pin into a piece about 4 inches in diameter.