Heat the oil in a large frying pan, add sausage and sage and sauté until crispy for 3-5 minutes. Reserve and keep warm.
In another pan mix grated Parmigiano cheese, single cream and milk; season with salt, pepper and nutmeg and cook until cheese is melted and sauce thickens for 5-6 minutes.
In the meantime cook the Tortelloni according to the package instructions and drain reserving a ladleful of the pasta cooking water. Add the pasta to the pan with sausage and stir gently, adding some of the pasta water if you need to loosen the sauce.
Divide Parmigiano fondue among 2 plates, top with Tortelloni and sausage, season with freshly ground black pepper and serve.