How to Make It
Cook the tortellini according to the package directions, adding the peas during the last minute of cooking. Reserve ¾ cup of the cooking water; drain the tortellini and peas and return them to the pot.
Add the radicchio, scallions, butter, ½ cup of the reserved cooking water, and ½ teaspoon each salt and pepper to the pot and toss to combine. (Add more cooking water as needed to loosen the sauce.) Serve with the Parmesan.