Bring approx. 3 litres of water to the boil in a saucepan. Add vinegar. Beat the eggs one by one into a cup. Make a whisk in the vinegar water and let the eggs slide into the whisk one by one.
Cook for about 4 minutes. Lift it out and let it drip off on kitchen paper.
Wash, clean and quarter the tomatoes and remove the seeds. Cut the flesh into fine cubes. Peel and finely dice the onion and mix with the tomatoes. Season with salt and pepper. Halve the avocado, remove the core, peel the flesh and cut into slices.
Sprinkle with 1 tablespoon lemon juice. Cut the ham in half and fry until crispy in a pan without fat. Wash chives, shake dry and cut into fine rolls.
Melt the butter. For the sauce, mix the egg yolks, yoghurt, 1 pinch of salt and 1 tbsp. lemon juice in a tall, narrow beaker with the blender until smooth. Slowly pour the butter into the egg yolk mixture. Continue to puree until a smooth sauce is obtained.
Halve the toasties and toast them. Cover 4 toastie halves with ham and eggs, drizzle with some sauce and sprinkle with chives. Spread avocados on the remaining toasties, add salsa, place eggs on top and sprinkle with sauce.