Joint a pair of young chickens, and put them on the fire in a large saucepan with a quart of cold water. Let it come to a boil slowly; when it reaches this point put in a couple of stalks of celery, three or four sprigs of parsley, a bay-leaf, and a couple of slices of onion. Season with a tablespoonful of salt and a scant teaspoonful of pepper. Simmer for half an hour, closely covered. As soon as the chicken is done - test it with a fork - take it from the gravy, and keep it warm over hot water while you make the sauce. Cook together in a saucepan two tablespoonfuls of butter and two of flour until they bubble; do not allow them to brown; when they bubble add to them slowly, stirring constantly, a pint of the strained gravy of the chicken. Let this boil for about two minutes. Mix in another bowl the yolks of two eggs, three tablespoonfuls of milk, a table-spoonful of melted butter, and a tiny pinch of red pepper, and add this carefully, almost drop by drop, to the hot sauce, stirring all the time. Do not let the sauce boil again, but when it is thoroughly mixed put in a teaspoonful of lemon-juice; pour the sauce over the chicken and serve it at once.