We had several good dishes at Pucara in Cusco - right off of the Plaza -Armas. It's a small restaurant run by Japanese Peruvians - offering local Andean food in a rustic setting. No floor show so it's relatively quiet - you can actually hold a conversation without yelling. I loved their garlic soup - had it twice. The plain broiled trout is also expertly cooked (not dry) and I thought they did a pretty good version of arroz con pollo. Sadly, the desserts were not up to the standards set by the savory dishes.
Pucara. Plateros Calle 309 Just West of the Plaza de Armas. Cash only.