Using the lift at Pelvoux helps you to gain height quickly at the start of this tour, and gives you a leg up to make this a very doable day trip.
Park at the Pelvoux ski station and buy a rando pass, giving you a one-way ticket to the top of the resort (2 chairlifts). At the top of the first lift take the chairlift on the right - the Télésiège de la Crête.
At the top of the second lift, with skins on, head away from it up a gentle slope westwards that kicks up just before the Croix du Chastellet. From the cross follow the ridge. After a couple of hundred meters drop off the ridge to the left into a bowl. It is possible to continue over the ridge.
From the bowl traverse up and to the right(north-west) and rejoin the end of the ridge. There is a sign here in summer, but this may be buried under the snow. Go straight over in line with the ridge (west). The route heads up for some distance and then bears right (north) to take you onto the main face of La Blanche. Once on the main face - if you look up - you should see a steep band of snow between the rocks which leads to a col. Ascend this and from the col head rightwards (north-west) up to the summit.
From the summit, head back down to the col, down the snow band and back onto the main face. Ski leftwards on some easy angled slopes, then turn and head down the steeper slopes. There are many options for descent on the face, just be aware that there are some cliffs and gullies on the way down so keep your eyes open. As you near the bottom you should see the lake/reservoir which serves the Pelvoux ski resort. Head towards it and follow the track that runs alongside it and takes you back into the resort. At the end of the track, you join the piste next to the Resto Bar, the perfect place to stop for a drink before skiing down the piste to the parking.