For the hollandaise, place the egg yolk, lemon juice and a little salt in a tall mixing bowl and blend until smooth with a hand blender. Melt the butter. While the hand blender is running, slowly pour into the egg yolk mix.
Season with salt and pepper. Stir in crème fraiche and mustard. Warm up the hollandaise (do not boil!), keep warm.
Dab steaks dry, cut off the fat edge. Cut each steak in half crosswise. Heat oil in a pan. Sauté the steaks in it for about 1 minute on each side. Season with salt and pepper. Then fry each side over medium heat for a pink steak (medium) for 2-3 more minutes.
Wrap in aluminium foil and leave to rest.
1 1⁄2 Bring 2 l of water to the boil in a wide saucepan. Wash parsley, shake dry, chop leaves finely. Cut bread slices in half. Pour vinegar into the boiling water. Beat the eggs one by one into a cup, slide them into the water and poach in it at low heat for about 7 minutes.
Lift out and let it drain. Put 1 steak, 1 poached egg and some hollandaise sauce on each half of bread and sprinkle with parsley.