Cut heads of celery into pieces six inches long, leaving them attached to the root; remove the coarse branches, and trim the roots neatly. Parboil it for five minutes. Make a brown roux, using the butter and flour, salt, pepper, and nutmeg. Add the stock when the roux is well browned; and in this, place the bunches of celery; cover and cook very slowly for twenty-five minutes. Remove the celery, and place it evenly on a dish. Strain the gravy; pour it around or over the celery.