Process dried chiles and soaking liquid, jalapenos, ginger, garlic, shallots, nuts, and 1/4 cup of chicken stock to a smooth paste. Heat oil in a large pan and saute spice mixture over moderate heat for 2 minutes. Add mustard seeds and stir for 1 minute. Add chicken and fry over low heat for 5 minutes. Add balance of stock, lemongrass, rice vinegar, soy sauce, salt and potato. Combine well. Add jalapeno and tomato and cook, covered until chicken is tender about 20 minutes. Serve with rice.