In a large skillet, melt the remaining 2 tablespoons of butter. Add the chestnuts and cook over moderate heat, stirring occasionally, until lightly browned, about 4 minutes. Add the sliced celery and ras el hanout, season with salt and pepper and cook until the celery is crisp-tender, about 2 minutes. Add the stock and cook until the liquid is nearly evaporated and the vegetables are glazed, about 8 minutes. Keep warm.