Beets are peeled and boiled until tender. Cut into cubes. Peeled and boiled potatoes also cut into cubes. Combine the potatoes and beet and stirred. In separate bowl mix yogurt and mayonnaise. Mix until completely homogeneous. Add lemon juice, salt and dill to taste. While the potatoes and beets are still warm, pour with milk-mayonnaise mixture. Stir and leave to cool and to stand for 2-3 hours before serving.