In fry pan add a small amount of oil. saute onion, celery, potato and carrots. Depending on how much turkey you have leftover and how many pies you are making will depend on how many carrots and potato's you will need. I usually use about a cup for each large pot that I make which makes about 2 pies.
Cover with just enough water to barely cover vegetables. Cook until tender. You do not need to drain the water.