Grate the potatoes and the fresh Pecorino Toscano PDO coarsely and place them in two separate bowls. Press the grated potato well to remove the excess water. Place a pan over the heat with a knob of butter; when the butter is melted, form a disc with the grated potatoes, add a layer of Pecorino Toscano, and complete with another layer of grated potatoes. Cook each side over medium heat for about 7 – 8 minutes, taking care that the rösti adheres to the pan. When the potato is golden brown and the cheese has melted, your rösti is ready. Serve it hot with yogurt sauce and parsley.