Filling: Melt butter in skillet and over med.high heat, saute mushrooms with salt and a pinch of pepper until mushrooms are browned and liquid has evaporated. Remove one tablespoon. mushrooms to add to the sauce and reserve the rest for filling the 'kotletki' Patties: In a large bowl, mix together 1 cup of the breadcrumbs and the cream, combine with the chicken, egg, salt and a pinch each of the cayenne, nutmeg and pepper. Spread remaining crumbs in a shallow pan. Divide chicken mixture into 8 portions. With wet hands, form each portion into an oblong patty. Flatten slightly amd in center, place 0.125 of the mushroom filling. Fold over and pat chicken around filling. Roll each patty gently in bread crumbs and place on waxed paperlined tray. Repeat with remaining chicken and filling to make 8 patties. Cover and chill the patties. Recipe can be prepared ahead up to this point. In 1 large or 2 med skillets, heat together butter and oil. Arrange patties in a single layer and saute over medium heat for about 5 minutes on each side, adding more butter if necessary, until patties are golden brown. Sauce: Meanwhile in a small saucepan, melt butter and cook onions without browning for 2 3 minutes. Add cream, increase heat to high and cook, stirring constantly, until cream thickens slightly. Reduce heat to low, add vinegar, sour cream and salt. Heat through, but do not boil. Add reseved mushroom filling. Taste and adjust seasoning. Serve each kotletki napped with a spoonful of sauce, and garnished with watercress Accompanyed by Kasha..