Blanch peas in salted boiling water for a couple of minutes (more if fresh) and drain. In a non-sticking frying pan melt the butter; add ham, peas, sage, and cook for a few minutes until ham is lightly crispy. Season with salt and pepper to taste.
In the meantime, cook the tortellini according to package instructions and drain, reserving a ladleful of the pasta cooking water. Add the pasta to the pan and stir gently, adding some of the pasta water if you need to loosen the sauce.
Serve with grated Parmigiano Reggiano cheese.