Melt the butter in a large frying pan over a medium heat until it begins to sizzle. Add the peas and ham and cook, stirring, for 3–4 minutes if using fresh peas, or just 1 minute if using defrosted frozen peas.
Stir in the crème fraîche, add the nutmeg and season with salt and pepper. Bring to the boil and boil for 2 minutes until slightly thickened.
Cook the tortellini in a large saucepan of salted boiling water according to the packet instructions until it is al dente. Drain and toss into the creamy sauce with the Parmesan. Gently stir to combine and serve at once with a scattering of Parmesan.