Preheat oven to
450 degrees F. Line a large baking sheet with parchment paper. Combine
potatoes, 1 cup vinegar, and 1 Tbsp. salt in a medium saucepan. Add
enough water to cover by 1 inch. Bring to a boil, then reduce heat and
simmer until potatoes are tender, about 20 minutes. Drain and return
potatoes to saucepan. Add butter and gently toss to coat. Transfer
potatoes to prepared baking sheet, spreading them out in a single layer.
Using a heavy mug or glass, smash each potato to about ½ inch
thickness. Bake for 20 minutes. Remove potatoes from oven and turn over
each with a spatula. Drizzle with olive oil and continue baking for 20
minutes more. Once baked, sprinkle with 2 Tbsp. malt vinegar and
additional salt and pepper.
