Potatoes are a cornerstone of the Peruvian diet, and for good reason: They have been cultivated in the Andes for more than 8,000 years, and the country boasts a whopping 3,000 varieties of the tuber, which comes in a myriad of shapes, colors, and sizes. In the regional capital of Huancayo, creamy, gently spiced cheese sauce is usually poured over the potatoes or served as a dip. To really highlight the potatoes (purple-fleshed ones look especially dramatic), we serve them over the sauce…