After few years, six actually, I returned to Lac Blanc. Last time I was there doing Tour the Mont Blanc trek. This time I started gently from La Flégère taking cable car from Les Praz. There are two options, two trails that lead to Lac Blanc and I do recommend not the obvious/popular one for two reasons. First of all crouds on the main trail may be a pain during season. Many people take this route because it is the shortest one so with a bit of luck you can do it after luch. Second reason are the views (see below) which are way better on alternative trail including Lacs des Cheserys which are beautiful.
From La Flégère follow trail to Chalet des Cheserys and Lacs des Cheserys (along Montagne de la Flégère). When you reach crossroads which I marked red on map follow sign and trail to Lac Blanc. Just before Lac Blanc there is one difficulty, the ledder, which anyway is more comfortable to ascend not to descend. It’s only few meters high. From Lac Blanc follow sign to La Flégère which is the popular route and if you started early you’ll be passing all crouds going up. The whole corcle is about 10km and might take with no rush between 4-5 hours.