Whisk egg yolks, Dijon, vinegar, salt, and pepper together in a bowl (plastic or glass).
Add the oil a little at a time while whisking.
Add oil until you have a very thick mayonnaise.
Add crème fraîche, honey, and curry powder and mix well.
Season to taste with salt and pepper.
Cut eggs and apples into cubes.
Chop onions, capers, and cornichons roughly.
Mix everything together with the mayonnaise.
Refrigerate until ready to serve. It can advantageously be made a day in advance to let the curry flavor develop more.