Photograph: Martin Poole
Cook the potatoes in a large pan of boiling water until just tender. Drain the potatoes and set aside until they're cool enough to handle, then use a small knife to remove the skins (or leave the skins on, if you prefer). Allow the potatoes to cool completely, then cut them into chunks.
Meanwhile, dry-fry the bacon lardons in a small pan until crisp, then drain on kitchen paper. Combine all the dressing ingredients in a jug and blitz with a hand blender until smooth; season with plenty of black pepper.
Toss the dressing through the potatoes, then gently stir through half the spring onions and half the lardons. Tip into a serving bowl and top with the remaining spring onion and lardons.