Mix the cream and sour cream in a bowl until smooth.
Peel and quarter the apple and cut into small slices. Peel the onions and cut into rings, slice the cucumber and mix with the apple and the sour cream. Season well with pepper and vinegar or possibly cucumber water to taste. Chop the dill, fold in.
Rinse the matjes and cut into bite-sized pieces, then stir into the sauce. Season again to taste, possibly add a little salt. Let it steep for a few hours.