Rub the potatoes then cook them in lightly salted water. Rinse under cold water, drain and let them cool.
Mix the vinegar with the mustard and the oil, then season with salt and pepper. When the potatoes are luke-warm, cut them in half and put them in a large bowl. Drizzle over them the dressing.
Meanwhile, put the eggs in a pan of cold water. Bring to the boil, cover and turn off the heat. Leave them for 6 minutes, then drain and rinse under cold water. Peel the eggs, then chop them roughly into small pieces. Add them to the potatoes.
Chop the gherkins and spring onions into small cubes pieces, add these to the potatoes.
Mix the mayonnaise with the yoghurt to your liking. Drizzle this over the salad. Combine gently, taste and adjust the seasoning.
Scatter on top the herbs just before serving.