Halve any large potatoes. Cook potatoes and fresh peas, if using, in a large saucepan, covered, in boiling water for 10 minutes. Add frozen peas, if using. Return mixture to boiling. Cover saucepan and cook vegetables 2 minutes more or until potatoes are tender. Drain. Return potatoes and peas to the saucepan.
Add margarine or butter or parsley, and season to taste with salt and pepper. Stir gently (if potatoes are stirred too vigorously, their delicate skins may rub off) until butter melts. Makes 6 servings.