Soak dried cherries in boiling water for about 15 minutes. Drain. Saute onion in butter until soft. Turn off heat and mix in breadcrumbs, watercress, cherries, and enough stock to just wet the mix. Add a pinch of salt and freshly ground pepper. Stuff in to the cavity of a bird or inside a boned leg of lamb before cooking. Or, bake stuffing in a baking dish covered with aluminum foil for about 30 minutes at 350 degrees. Let stand for 10 minutes. Top with chopped dill and serve with a small spoonful of sour cream.