One of the world's oldest blue-veined cheeses, Gorgonzola PDO (Protected Designation of Origin) is the pride of Italy’s north. Produced in the regions of Piedmont and Lombardy (there are 15 provinces of production in total), the ‘king of blue cheeses’ is said to have originated in the 9th century and to have taken its name from the town of Gorgonzola, one of its original production centres just outside Milan. Straw-white, it comes in two varieties: creamy, soft, sweet Gorgonzola PDO dolce, and the stronger, spicier, more crumbly Gorgonzola PDO piccante. Made with whole pasteurised milk from the region’s cows, with no additives or preservatives, Gorgonzola PDO dolce is matured for a minimum of 50 days and a maximum of 150 days; the piccante, a minimum of 80 days and up to a maximum of 270 days. A favourite in kitchens worldwide, its production is a rarefied process known only to a few. Here are the must-visit locations to indulge in the delicacy and learn more about the 'king of blue cheeses'.