1. Peel the potatoes, cut them into small pieces and place in a saucepan with 18 fl oz (500 ml) water and 1/2 tsp salt.
2. Bring to the boil, cover tightly and cook over a low to moderate heat for about 15-20 minutes or until the potatoes are tender and have absorbed all the water.
3. Chop the hard-boiled eggs coarsely; trim the spring onions, removing the outer layer, and slice the bulb and leaves into rings. Use a fork to partially break up the hot, cooked potato pieces. Leave to cool at room temperature.
4. Make the mayonnaise, stir in 3 tbsp soured cream or smetana and mix with the potatoes, the spring onions and chopped eggs. Season with salt and freshly ground pepper to taste.
5. Serve at room temperature, with green salad, as an appetizer or as part of a cold lunch.