Put 2 Tablespoons of butter in an oven proof skillet. Saute onions, carrots, and celery. Add salt and pepper. After vegetables are tender add flour. Cook 2-3 minutes, add chicken broth, soup base, corn and turkey.
Take off the heat and spread mashed potatoes over the top. Top with cheese and bake in a preheated 350* degree oven until heated through and cheese melts.
If you don't have any left over mashed potatoes make a pie crust and put over the top. Cut slits and bake in a 400* oven until golden brown.