There are a number of quite decent restaurants within walking distance of Stazione Centrale before you get on the bus/train to Malpensa. I like Osteria del Treno very much (very traditional Milanese dishes and slow food products), Tratttoria dalla Zia is a good Tuscan style steak house and da Oscar is a somewhat kitschy place with decent food and huge portions (steak and pasta). For something a bit more refined Delikatessen is a nicer northeastern Italian restaurant.