Stir egg yolks, lemon juice and a little salt in a high mixing bowl with a hand blender until smooth. Melt the butter and pour it slowly into the egg yolk mix while the hand blender is running. Stir in crème fraiche. Season with salt and pepper.
Cut the vanilla pod open lengthwise. Scrape out the pulp with the back of a knife. Stir vanilla pulp or powder into the hollandaise sauce. Carefully heat up the hollandaise (do not boil!) and keep warm