Chinese Bbq'd Pork Bun (Cha Siu Bow)

Preparation : Mix together the warm water, 1/2 tsp. sugar and yeast in an 8 oz. measuring cup. Let stand until it rises to the 8 oz. level (about 20 minutes). Sift flour, cake flour, sugar and salt into a large mixing bowl. Add shortening, yeast mixture and mil,. Knead mixture 5 minutes to form a dough. Cover with a damp cloth and set dough in a warm place. Allow the dough to rise for 3 hours. Heat wok, add oil and stir-fry pork for 2 minutes. Add 2 tablespoons water, salt, sugar, soy sauce, oyster sauce and hoisin sauce. Bring it to a boil. Prepare thickening by mixing the cornstarch and 4 tablespoons cold water. Stir into the mixture and cook for 1 minute. Let cool before using. After 3 hours, when the dough has risen, shape into rolls about 2 inches in diameter. Cut each roll into 1-1/2 inch pieces. Shape each piece into a shallow bowl shape. Put 1 tablespoon filling in the center, close and twist dough to form a bun. Put the bun on a 2 inch square of white paper. (This prevents the bun from becoming soggy while steaming.) Place 8 buns in a pie pan and allow them to set and rest for 15 minutes in a warm place. Steam for 25 minutes.