In a medium skillet, melt the butter over medium low heat. Add the onion and saute until transparent, about 5 minutes. Stir in the green peas and the broth, and cook for about 3 minutes. Add the snap peas, snow peas and parsley, and season to taste with salt and pepper. Cook, covered, for about 3 more minutes.
Remove the inner leaves from the radicchio and spread the outer leaves out to make a bowl. Fill the hollow with the pea mixture and garnish with additional Italian parsley.
