Sauté the mushrooms in 1 tablespoon of butter until they have released their liquid and begin to brown. Set aside.
Dice the carrots and celery and chop the leeks. Melt five tablespoons of butter in a large sauté pan, then add the vegetables with 1 tsp salt. Stir to combine. Cook over medium heat, frequently stirring until the vegetables are softened but not brown.
Sprinkle the flour over the vegetables, mix to coat and cook for about 1 minute, stirring constantly. Then, add the stock, and bring it to a simmer. Add the cream and wine and bring to a gentle boil. Turn off the heat and set aside.
Add the mushrooms, peas, parsley, and turkey meat to the sauce mixture and stir gently.
Transfer the filling to a buttered ovenproof casserole dish.
You can cook a pot pie in several ways. A pastry crust can be layered over the filling, crimped at the edges, and pierced in four places to let steam out. Cook in a 375-degree oven until the crust is golden brown and you see some bubbling filling through the steam holes. This should take between 45 minutes to 1 hour, depending upon your oven and the temperature of the filling when you put the casserole into the heated oven.
Another option is to cook the filling without a pastry cap. Cover with foil and cook at 375 for 30 minutes. Remove the foil and cook for 15 minutes or until the casserole bubbles.
Then, top each serving with a precooked biscuit or 3 “square of cooked puff pastry.