GARNISH: cherry tomatoes or broccoli florets, more grated Parmesan cheese, and sprinkling of freshly ground black pepper, optional. Boil a large pot of water; cook pasta until al dente. While pasta is cooking, in bowl of food processor, place ricotta, yogurt, margarine, garlic, walnuts, and chhese; process till smooth. Stir in remaining ingredients. When pasta is done, drain well. Toss with sauce. Top with garnishes and serve immediately. VARIATIONS: when sauce is tossed with pasta, add steamed vegetables such as peas, broccoli, cut green beans, and spinach ~ serve cold as pasta salad ~ for Fettucine Almost Alfredo, substitute quarter cup milk and quarter cup vegetable stock for the yogurt; omit garlic, walnuts parsley, and basil; garnish with almond slices, parsley sprigs, and cherry tomatoes or cut steamed asparagus