Preheat oven to 350°F
In a large cast iron skillet, melt the butter or ghee.
Add the chopped onions and cook until soft. 3-5 minutes.
Slowly add the potato starch, making sure that each addition is fully absorbed into the melted butter.
Slowly add the chicken or turkey stock. Stirring until smooth before adding more. Be sure to get all the lumps out. You can not get them out later.
Add the turkey and vegetables. Remove from heat and pour into a prepared casserole dish.
Top with mashed potatoes.
Bake in a 350°F oven until the gravy begins to bubble and the potatoes become golden brown. About 40 minutes.