Although not at long as the other lines described on Cairn Toul, this descent takes you into one of the most beautiful corries in the Cairngorms. The face comprises of a number of shallow runnels, separated from each other by shallow rocky ridges. Your choice of descent on the day should be dictated by the snow cover.
One of the runnels directly below the summit is the best one, with a relatively consistent gradient all the way down to the shallow ridge above the lochan. Set off from the cairn at the North end of the Cairn Toul summit ridge. After a few metres, you should be able to ski left around, and then below some rocks (effectively doing an about turn), bringing you into the runnel. The way down from there will be obvious. An alternative, depending upon snow cover, is to ski down the North ridge some way before dropping into a complete runnel.
It is worth having a look at the face prior to skiing it to ensure you don't cut down the wrong runnel - those nearest the summit often have rocky sections. You can look across the face from the col between Sgor an Lochain Uaine and Cairn Toul to give you an idea of the snow cover.
If you want to re-ascend Cairn Toul from the corrie, you can scramble up the scree covered North ridge of Cairn Toul, or find your way up to the col between it and Sgor an Lochain Uaine, where there is usually a break in the cornice. The striking Northeast ridge of Sgor an Lochain Uaine is a very good ascent, although be aware it can be a little tricky at the top. If you don't want to climb back out, you may be able to continue on down into the Lairig Ghru following the often present line of snow that sits in a channel below the face, bounded by a shallow ridge above the lochan. At the end of this channel, long lasting snowfields descend towards the Lairig Ghru.