There were, and still are, great restaurants all over Europe, but the greater part of Blue Trout and Black Truffles is devoted to the eatingplaces and vineyards of France. It is a vicarious experience to read about the culinary wonders of the notable establishments of another era that have become the last epicurean haven in this materialistic, mechanized world of fastfood chains and frozenfood dinners. Mr. Wechsberg reaches back to the twilight days of the Habsburg monarchy, when those splendid monuments to the haute cuisine in central Europe, Meissl and Schadn of Vienna and Gundel's of Budapest, were in their prime.