Wash the potatoes thoroughly and cook covered in water for 15-20 minutes. Peel and finely chop the onion. Boil up broth, onion, vinegar, oil, mustard, some salt, pepper and sugar in a pot. Remove from heat and pour into a large bowl. Drain the potatoes, rinse with cold water and cut in half.
Add potatoes to the hot marinade. Leave to soak for at least 1 hour, turning occasionally. Clean and wash the salad and pluck into bite-sized pieces. Halve the avocado, remove the core, remove the flesh from the skin and cut into thin slices. Turn the slices in lemon juice. Add lettuce and avocado to the salad just before serving. Season again with salt, pepper and sugar. Cut roast beef slices in half. Arrange salad on plates.
Turn the slices in lemon juice. Add lettuce and avocado to the salad just before serving. Season again with salt, pepper and sugar. Cut roast beef slices in half. Arrange salad on plates. Spread slices of roast beef on top
waiting time approx. 1 1/4 hours