On augille du MIDI..From the bottom of the snow arete from the snow tunnel head down the steep face facing down toward the Vallee Blanche (a good place to make some warm up turns). From the bottom of this face head around the cliffs to the right until you can see the Cosmiques refuge. Side step or hike up to the col between this refuge and the Simond Refuge (smaller building on the right). A little bit to the left on the col you find the start.
Unless the snow conditions are perfect you will have to make three long abseils into the Couloir (although it can be possible in the spring to ski straight in). There is a bolted belay on the rocks at the top and then two more belays on the right bank 30m appart. After putting your ski’s on you will find yourself on the steepest section and exposed over a small cliff band. Make you way down carefully trending leftward to find a small awkward section to cross this steep section. The skiing from under this cliff is about 45° and with good snow it is superb. Go back on the Bosson glacier to either the midstation or ski down to the montblanc tunnel.
Serious skiing. Bring cord and harness. Crevasses!