In large saucepan cook macaroni according to package directions; drain and return to saucepan.
Meanwhile, in a small saucepan heat butter over medium heat until melted. Add onion; cook and stir about 5 minutes or until onion is tender. Remove saucepan from heat; add wine to onion mixture. Return to heat. Simmer, uncovered, about 5 minutes or until most of the wine has evaporated. Remove from heat.
Gradually add the Gruyere cheese and fontina cheese to hot Mac and Cheese Base, cooking and stirring over low heat until mixture is smooth and cheeses are melted. Stir in the onion mixture.
Stir cheese mixture into the cooked macaroni. Cook and stir over low heat until mixture is heated through. Remove from heat. Let stand for 5 minutes (mixture will thicken upon standing). Serve immediately.