Put the cranberries in a small bowl with the flour, mix well and set aside.
Heat the oil in a large saucepan and cook the onions for 5 minutes, until softened. Add the mushrooms and most of the thyme, then continue to cook for a further 10 minutes, stirring occasionally.
Add the turkey and gravy (or stock), cranberries, nutmeg and crème fraîche. Season with freshly ground black pepper, then cook gently for 5 minutes.
Meanwhile, cook the tagliatelle in a pan of boiling water for 2-3 minutes. Drain. Serve topped with the stroganoff and garnished with the parsley and remaining thyme.