Preheat oven to 400 degrees. Peel and boil the sweet potatoes and garlic in water until soft. Drain the potatoes. Mash with chicken broth, milk, sour cream, salt and pepper. In a large sauté pan brown the turkey. Once the turkey is cooked, set aside on a plate lined with paper towels. Add the olive oil to the pan, then add the onion and celery. Season with salt and pepper. Cook about 12 minutes, until celery is soft. Add the garlic and mushrooms, sauté another 3-4 minutes. Add the flour, salt and pepper and mix well. Add in the frozen vegetables, chicken broth, tomato paste, Worcestershire sauce, rosemary, cooked turkey, and mix well. Simmer on low for about 5-10 minutes. Pour into an oven safe dish and top with the mash potatoes. Bake for 20 minutes or until potatoes turn golden. Remove from oven and let it cool 10 minutes before serving.