In the morning boil 454 grams Jersey Royal new potatoes for 15-20 minutes in salted water until tender. Drain, cool, and leave in the fridge to chill.
Hard boil the eggs, if using, and cool.
Leave the potato skins on the potatoes, if you wish, and cut the cold potatoes into 1 cm cubes. Cut the 2 hard boiled eggs into small pieces too, if using.
Add 0.5 small red onion, finely chopped, 2 gherkins, chopped, and 1 stick celery, finely chopped. Toss gently to combine.
Combine 85 ml mayonnaise, 85 ml plain natural yoghurt, 1 tsp dry mustard powder and 1 small garlic clove, finely chopped, together in a small bowl and season well to taste.
Spoon over the potato mixture and toss gently to combine well.
Stir in 2 tbsp fresh parsley and 2 tbsp fresh chives, taste again and season to taste with Shetland sea salt and freshly ground black pepper (I like a lot of salt and pepper in my potato salad). Chill until needed.