Preheat oven to 375 degrees F. Grease a 3-quart rectangular baking dish; set aside. In a 12-inch skillet cook ground turkey and turkey sausage over medium heat until brown, using a wooden spoon to break up meat as it cooks. Remove cooked turkey and turkey sausage from skillet.
In the same skillet heat 1 tablespoon of the butter and the 2 tablespoons oil over medium heat until butter is melted. Add celery and yellow onion; cook until vegetables are tender, stirring occasionally. Stir in flour, herbes de Provence, and 1/8 teaspoon of the pepper. Gradually stir in broth and evaporated milk. Cook and stir until bubbly. Stir in cooked turkey and turkey sausage. Transfer mixture to the prepared baking dish.
Meanwhile, in a large skillet heat the remaining 2 tablespoons butter over medium heat until melted. Add cabbage, green onions, and the remaining 1/8 teaspoon pepper. Cook just until cabbage is tender, stirring occasionally. Stir in mashed potatoes; heat through. Spread potato mixture evenly over turkey mixture.
Bake, uncovered, for 35 to 40 minutes or until heated through. Let stand for 10 minutes before serving. If desired, in a small saucepan cook shallots in the 1 tablespoon oil over medium heat about 5 minutes or until golden. Sprinkle shallots over potato-topped pie.