In a large saucepan of simmering water, cook the potatoes for about 20 minutes, or until tender; drain.
Preheat the oven to 450°F. Line a rimmed baking sheet with parchment paper.
Place the potatoes on the prepared baking sheet. Using a clean, folded tea towel, crush each potato using your palm. Drizzle with olive oil and malt vinegar, and sprinkle with salt and pepper. Bake for 25 minutes, or until crisp and golden.
Drizzle the potatoes with extra malt vinegar, if desired, for serving.