Trim and remove the strings from the celery and cut the celery diagonally into 1/2" pieces. In a skillet combine the celery, chicken stock, butter, sugar and bring to a boil; cook over moderately high heat, stirring occasionaly, until it is reduced to a glaze. Reduce the heat to moderate,stir in the cream and mustard and cook the mixture, stirring, until the cream is thickened slightly. Season with salt and pepper, transfer to a heated serving dish and sprinkle with parsley leaves. Serves 6 .