LAY 2 SLICES OF HAM on 1 side of the butterflied breast. Refold the breast, enclosing the ham. Lay the breast on a sheet of caul fat. Roll up tight. The caul is sticky, so it needs nothing to seal it. Dust the surface with water chestnut powder, flour or cornstarch. Shake off the excess. Heat the oil in a wok to 350F (moderate). Slide the chicken breasts into the oil, 1 by
1. When they have browned (about 5 minutes), remove 1 from the oil and press it. If it feels mushy, it needs more cooking. Remove and drain the chicken. Slice the chicken, crosswise diagonally, into 1/2-inch pieces. VEGETABLE SAUCE: Heat the oil in a wok and flavor with garlic and ginger. Remove the garlic and ginger and add the water chestnuts, bamboo shoots and scallions to the wok. Stir-fry for 30 seconds, then add soy sauce, wine or sherry, and chicken broth. When the liquid boils, stir in the dissolved cornstarch to thicken the sauce. Spread the sauce on a platter as a bed for the sliced chicken breast.