Add the remaining 1/2 tablespoon of butter and the scallions to the skillet. Cook over moderately low heat, stirring, for 1 minute. Add the whiskey and carefully ignite it with a long match. When the flames die down, add the cream, mushrooms and any juices from the scallops. Simmer the sauce until slightly reduced. Add the scallops to the sauce, season with salt and pepper and serve.