Saute the fresh carrots,onion, celery and mushrooms until tender in a large pot.
Blend the soft butter and the 2 T. flour into a paste.
Pour the stock into the pot with the veggies. Bring to a simmer.
Stir in the flour/butter past, stirring constantly.
When the mixture is the thickness you want, put in the peas and turkey.
Lightly grease a 2 quart casserole dish, pour in the mixture.
Preheat the oven to 350°F.
Now, if your leftover mashed potatoes are too stiff, add some milk and an egg to loosen them a bit. Spread over the turkey covering completely. I like to add chives to the potatoes for an extra flavor.