In 25 cm non-stick skillet, heat oil; saute onions and garlic until tender. Add reserved clam juice, half c evaporated skimmed milk, salt and pepper. Cook uncovered over medium heat for 5 minutes, stirring occasionally. In small bowl, gradually stir remaining half cup evaporated skimmed milk into cornstarch. Add to skillet, stirring constantly, until sauce thickens. Add clams; heat. DO NOT BOIL. Toss hot pasta with tomatoes, basil and sauce.= Garnish with basil leaves if desired.