Boil the potatoes in water with a pinch of salt until soft (about 10-15 min depending on the size of your potatoes).
While the potatoes are boiling, peel and chop the onion finley. Combine the mustard, sugar, gherkin liquid, vinegar, and chopped onion in a jar. Screw on the lid and shake thoroughly to create the vinaigrette.
Peel the apple and chop into little (1 cm) chunks cube the gherkin/pickles.
While still warm, peel of the skin and chop the potatoes in about 1 cm wide slices.
Place the potatoes, apples and gherkins into a larger bowl. Pour over the vinaigrette and mix carefully with a wooden spoon. Leave the warm potatoes to rest in the vinaigrette. This will help the potatoes to absorb the flavour. Season with salt and pepper.
I recommend you leave the salad in the fridge for at least 4 hours for the flavours to develop. Alternatively, you can also leave it to rest overnight.
Before serving stir in the chopped spring onions and garnish with chopped herbs.
Serving suggestion: as a side of grilled sausage and meat