Heat the oil in a large frying pan; add sausage, sage, and sauté until crispy for 3-minutes. Reserve and keep warm. In another pan mix grated Parmigiano Reggiano cheese, single cream and milk; season with salt, pepper and nutmeg and cook until cheese has melted and sauce thickens for 5-6 minutes.
In the meantime, cook the Tortelloni according to package instructions and drain, reserving ½ cup of the pasta cooking water. Add Tortelloni to the pan with sausage and stir gently, adding pasta water a little at a time if you need to loosen the sauce.
Divide Parmigiano fondue among plates, top with Tortelloni and sausage, season with freshly ground black pepper and serve.