To make biscuits: In mixing bowl, combine flour, baking powder, sugar, salt and cream of tartar.
Grate butter and mix with dry ingredients.
Carefully add buttermilk and mix until incorporated.
Fold over 5-6 times, roll out and cut into 10-12 rounds.
Place cut biscuits on floured surface.
Refrigerate 30 minutes.
To make turkey pot pie filling: Preheat oven to 375 F.
Heat large pot over high heat and add turkey fat.
Add onions, carrots, celery, bay leaf, garlic, thyme, salt and pepper; gently sweat.
Add 1/2 cup flour and cook 2-3 minutes.
Add turkey stock 2 cups at a time, allowing to thicken before adding more.
In bowl, mix remaining flour with turkey.
Add turkey pot, bring to simmer until thickened.
Add seasoning, to taste.
Add pot pie filling to casserole dish and gently place biscuits closely together on top.
Brush biscuits with melted butter and bake 25-30 minutes.
Remove from oven and cool 10-15 minutes before serving.