My version evolved from the first potpie recipe I found, in Julia & More Company. That was for a rabbit and leek potpie. In the years since, I've changed everything but the crust, which is a buttermilk biscuit. A very large buttermilk biscuit, as the potpies fill lasagna pans. But, of course, you can substitute any savory pie crust you like. Or even mashed potatoes. This is very much an ad lib recipe, with the quantities up to you.
Friday morning, debone all the leftover turkey. If you're planning a big leftover party, be sure to have roasted an extra bird. Refrigerate.
If you don't have chicken stock or turkey stock on hand, make some, the more the better.
If you've have roasted root vegetables left over, save them for the pie, too. Leftover simple greens as well.
On Saturday (Friday is too soon for eating elaborate leftovers), cut into chunks: carrots, celery, celery root, rutabaga, turnip. You pick. Slice some leeks and garlic.
In a large casserole, heat up some olive oil and butter and sauté the leeks until they soften. Add the garlic. Cook three more minutes, stirring. Add the chunked root vegetables and turn to coat. Add salt and some herbs like thyme, marjoram and rosemary. Lower heat, cover and let sweat until soft. Meanwhile heat up the stock.
Uncover, raise heat a little, add some more butter to melt and then sprinkle with flour, stirring, to make a roux. (You'll need about 3 tablespoons of flour for every 2 cups of liquid.)
When the flour is well absorbed, slowly add the hot stock, stirring as it thickens. Let simmer over low heat, stirring often. Slowly dribble in white wine. Adjust salt. Let simmer some more until the flour taste is gone. Add the cooked leftovers (turkey, roasted vegetables, greens) and stir.
Pour into a large lasagna pan (or pans), cover with the crust and bake.