I had a couple of pre-made pie crusts I bought on a whim.  We went with a beef filling that included carrots, onions, potatoes, and mushrooms.  The beef was from an all day simmer in the crockpot, the mushrooms, onions, and celery were sauteed in olive oil, and the potatoes and carrots were both boiled until tender before being combined with Bisto gravy made with the water the veggies were boiled in.