Wash the potatoes, halving any larger ones, then cook in a large pan of boiling salted water for 15 minutes, or until soft. Drain well.
Spoon the yoghurt and English mustard into a large serving bowl with 2 tablespoons of extra virgin olive oil. Finely grate in the zest of the lemon, squeeze in the juice, mix well, then toss in the warm potatoes. Season to perfection, tasting and tweaking.
It’s fun to sprinkle this dish with edible flower petals, such as marigolds, violas or nasturtiums. Fresh herb flowers would also work a treat. Serve the potatoes hot, warm or cold.