For the cold sour cream soup, mix sour cream, mayonnaise and 200 ml whole milk in a bowl, dilute with a little additional whole milk if necessary, round everything off with fine sea salt and a little oil, then refrigerate for two hours.
In the meantime, cut the matjes and salmon into 1.5-2 cm cubes and chill them as well. Cut the beet into 1 cm cubes, drain on kitchen paper and chill.
Peel the apple, remove the core and cut the flesh into 0.5 cm cubes, immediately sprinkle them with lemon juice in a bowl (I add a little sunflower oil) and mix well.
Season the well chilled sour cream soup with a squeeze of lemon juice or vinegar, add a little salt if necessary. Arrange a small ladle of soup in deep plates (do not pour too much soup into the plates – it should be about 0.5 cm high in them). Place the diced maties, salmon, beetroot and apple decoratively in the soup (so that you can see all the individual ingredients) and serve immediately – the rest of the soup can be served separately in a sauce boat.