Clean the iceberg lettuce, cut into pieces that are not too small, rinse with cold water and drain well or spin dry. Drain the mandarins in a sieve, collecting the juice and measuring 4 tablespoons for the sauce.
Sort the raspberries. Gently mix the iceberg lettuce, tangerines and raspberries.
For the creme fraiche sauce, mix with lemon and mandarin juice and season with salt, pepper and sugar. Serve the sauce separately with the salad or stir carefully into the salad just before consumption.