Russian
Boil the potatoes in their skins for 20 minutes and the eggs for 10 minutes, then cool both completely.
Peel the potatoes and eggs and cut them into small cubes.
Dice the ham, cucumbers and radishes to the same size, and finely chop the green onions and dill.
Mix everything in a large bowl with the mustard and salt.
Chill the mixture and the kefir for at least 30 minutes.
Divide the mixture among bowls and pour over the cold kefir just before serving; for the classic sour-sweet version, use chilled kvass instead.