Cook the pasta in salted water according to the instructions on the packet.
In the meantime, do not sear the sage leaves in butter too hot, pour in the cream and let it boil down briefly. Reduce the heat, stir in the parmesan and stir until the cheese is completely melted.
Season to taste with salt, pepper and nutmeg. Possibly add a little lemon juice, but then don`t let it boil anymore.