In a medium saucepan, combine the potatoes, vinegar, water, and salt. Add more vinegar and water in equal parts if necessary to cover the potatoes. Cover and bring to a boil over high heat. Cook for 30-40 minutes, or until tender.
Drain the potatoes and allow to dry (they’ll do this on their own in less than a minute since they’re hot) Dump them onto a parchment-lined rimmed baking sheet and drizzle with 2 tablespoons of the olive oil. Shake the pan so they’re well coated.
Use a small heavy pan or mug to flatten each potato – simply apply pressure downward until the skins burst and the potatoes flatten.
Roast for 20 minutes, or until they’re golden brown on the bottoms and then flip and drizzle with the remaining tablespoon of olive oil. Roast another 10 minutes or until they’re crisp on both sides.
Sprinkle with flaky salt and serve with sour cream, if desired.
Notes
If keeping kosher for Passover, use apple cider vinegar