For the croquette batter: In a heavy pot, heat the milk and chicken stock on the stove and then add the white pepper, fresh parsley and salt, if needed. In a separate heavy pot, melt the butter and add the minced celery. Stir in the flour and cook for 3 minutes. Pour in the hot milk and stock and stir until thickened and smooth. Fold in the chicken meat and allow to cool.
Breading the croquettes: Shape 3 ounce portions of croquette batter in the shape of a cone and place on a tray lined with waxed paper. Next make an egg wash from the milk, eggs and salt. Dip the croquettes in the egg wash and then into the flour and let stand a few minutes. Finish breading by dipping the croquettes back in the egg wash and then rolling in breadcrumbs.
For the chicken gravy: Melt the butter in a 1- or 2-quart saucepan, and stir in the flour. Pour in the stock and whisk until smooth. Bring to a boil, reduce the heat and cook for 20 minutes. Add the fresh parsley, white pepper and salt, to taste, (if fresh stock was used).
Cooking the croquettes: Fry the croquettes in a pot with salad oil or liquid shortening, heated to 350 degrees F, until golden brown, 2 to 3 minutes. Drain well and blot on paper towels. Place on a bed of mashed potatoes and top each croquette with chicken gravy.
Recipe courtesy of Chef Larry, The Dining Car, Philadelphia, PA