Peel the potatoes and slice in half lengthways. On the cutting board place the potato cut side down and place a wooden spoon handle along each side to make cutting easier. You don't awnt to cut all the way through. Cut down, making evenly spaced thin slices, just under 1/4 inch thick.
Put the vinegar and 2 tbsp of salt in a large saucepan. Add the potatoes. Bring to a boil and cook for 10 to 15 minutes. When just tender, drain and transfer to the baking dish, flat side down.
Drizzle with the olive oil being sure to brush it into the gaps and bake for 1 hour to 1 hour 15 minutes. They should be golden and slightly crisp. Drizzle with a little extra olive oil if needed to get that nice golden color.
Remove the potatoes to a serving plater and sprinkle with the sea salt flakes.