Soak the morels in 1 1/2 cups of boiling water until softened. Rinse and pat dry; reserve the soaking liquid. In a skillet, heat 1 tablespoon of the oil. Add the sausages, cover and cook over moderate heat until no longer pink within; slice 1/4 inch thick. Heat the remaining oil in the skillet. Add the shiitake, season with salt and pepper and cook until softened. Add the shallots and morels; cover and cook for 4 minutes. Add the water chestnuts. Pour in the morel soaking liquid. Add the sausages and simmer for 2 minutes. Stir in the tomato paste. Season with salt and pepper. Off the heat, swirl in the butter and sprinkle with parsley. Serve over polenta.