My guidebook said that the normal route was from Quebrada Cojup to the SW ridge and from there to the summit.
I decided to do it a bit different: I planned to over Huapi pass from the Quilcayhuanca side and try to follow the ridge from there, or pick up the normal route on the other side. However, when I approached the mountain, I saw that the pass was quite some ways from the summit, and the ridge didn't look easy either. I sort of decided to try to find a direct way from Quilcayhuanca to the ridge, closer to the summit. I had started from Quebrada Cayesh, and it took a bit more time than planned, so I ended up camping high on the glacier. With only 200m to climb, I could be on the summit early next morning, so I thought.
Thanks to the deep powder it took a few hours longer, but in the end, it all worked out. Later I read that I had more or less followed the route of the first ascent!
I descended the normal route to the Cojup valley. For a short section on the ridge, there was an old trail I could follow, but a bit lower the snow on the glacier was harder and the trail faded away. I headed down where it looked easy, roughly keeping to the west. On the talus below the glacier, I picked up a cairned trail coming down from the pass, and followed that down.
I met a small guided party doing the Quilcayhuanca - Huapi pass - Cojup trek. They were very surprised to see me, coming down from a different direction than the pass. They set up camp as soon as they reached the Cojup valley floor, while I continued down the valley, because I wanted to make it all the way to Huaraz. I was out of the Cojup valley by sunset. Half way from there to Huaraz, I came across the first houses, and was fortunate enough to find a taxi. My feet were very happy about that, as walking a long distance in stiff plastic mountaineering boots isn't ideal. My blisters healed quickly though.