This is the normal route to the Mont Billiat. The real ascent begins at the Chalets de Pertuis.
Chalets de Pertuis (1585 m) can be reached on a good footpath from Chalets de la Buchille. How to reach Chalets de la Buchille, see the main page.
Chalets de Pertuis can also be reached over Mévonne from Le Jotty (but long and boring forest trail).
From the Chalets de Pertuis, take the path (on the right if you come from Buchille) , direction the N ridge of Mont Billiat. You reach a little collar. On the left , nice view on a gully and the Mévonne rocks.
Cross the large comb with remaining snowfields. A cable secures the steepest part. On the right, you reach the grassy summit ridge and then easily the main summit.
If the snow remains in the summit comb crampons can be useful.