Mix together dry ingredients in a bowl. Add boiling water and stir until all of the water is absorbed. Rest the dough for about 10 mins so you won't burn your hands. When cool, knead the dough until it is smooth and feels like play dough, then work in the oil a little at a time.
Peel and devein the shrimp. Chop the mushrooms. Mince the pork fat. Mix everything together until filling becomes sticky, proceed to filling the dumplings.
Making the Dumplings:
Divide the dough into small pieces the size of a walnut.
Using a small rolling pin, roll the dough into a thin disk; roll the edges of the disk to make it thinner than the center.
Pleat and pinch half of the wrapper to form a small cup, fill the cavity with the shrimp filling.
Fold the other half of the wrapper over so it meets pinched edges and encloses the filling.
Steam 8 minutes and serve. Yields 12-15 dumplings.