Go up the Index chairlift and then the Floria ski tow. Descend the piste a short distance until it is possible to make a long, slightly descending traverse under the Tour des Crochues. (This can often be icy, or avalanche prone, in which case it is preferable to descend further down the piste and take a lower line around the shoulder.) Go around the shoulder under the ridge descending from this Tour. From here there will frequently be ski tracks making a rising traverse to the Lac Blanc and the Col de Belvedere and Col Beugeant ski tours. It is possible to go this way, going up towards the Belvedere from the lake until it is possible to turn left, WNW, up to the Col des Dards. (Marked in red on the photo.) However, a quicker way from the shoulder is to take a much higher line (N then NW) and making a undulating traverse into the glacier bowl just below the Col des Dards, (between the Aiguille du Belvedere and the Aig Crochues). (Marked in blue on the photo.) The ascent to the col should present no difficulties. (F, S2)
By the same route it is possible to go the N summit of the Aiguilles Crochues, more difficult, S3 near the top.

Alternative start
It is possible to start from the top of the Flegere cable car (1877m) To avoid going up the pistes it is better to descend to the foot of the Trappe chairlift by the green piste. From here follow a more peaceful route passing the points marked 1764m > 1912m > 2062m > 2171m on the IGN map before before joining the route from the Index to Lac Blanc.

Descent

The recommended descent is by the route via Lac Blanc. From there go to the Tête Aubuy and then the piste under the Chavanne chairlift , which leads directly to Flégère (and so to La Praz if there is enough snow)

Remarques

440 m height gain from Lac Blanc, plus a little more for the traverse. 990 of descent to Flégère.
Excellent non serious tour, other than the usual risks due to snow conditions. The traverse from the Index under the Tour des Crochues can be very icy in the morning.