Mix well the chicken, soup, stuffing mix, egg, onion, and celery. Refrigerate 3 hours minimum.
Create a 'log' shape from about 3/4 cup of mixture. Gently drop onto the counter to flatten the bottom to form a traditional 'cone' shape. (about 3 high, 2 in diameter), or form patties for a simpler method.
Roll croquettes in bread crumbs. (At this point, you can freeze them for up to two months or cover them and place them in the fridge overnight to serve the following day. Just bring them to room temperature when ready to use if frying them).
Fry in about 1/4 of oil in skillet over medium heat turning occasionally till golden brown on all sides and bottom, about 10-15 minutes. For a healthier version, they can be baked at 350F for about 25-30 min (from the freezer, bake 45-50 minutes). Keep warm in 200 degree oven.
MAKE THE SAUCE: Meanwhile, In a small saucepan, stir the remaining can of soup with milk, stirring until warmed and creamy.
Pour over croquettes or serve sauce on the side. Traditionally served atop a mound of mashed potatoes for a wonderful presentation.