Bruno Paolato is the cooking partner in Ai Mercanti, one of the Venetian restaurants where I feel most at home. I prefer to think of Bruno as a cook rather than a chef, a distinction that he, and his colleagues, may not find as flattering as I do. Never mind. The most satisfying source of Italian cooking is the home, rather than a professional academy, and I prize those restaurants whose food, however accomplished it may be, still t