Heat oven to 240C/220C fan/gas 9. Boil the potatoes until the softer side of cooked, about 12 mins. Drain, slice in half, then tip into a bowl.
Tip the capers, olives and herbs on top of the potatoes, then add most of the oil and a little seasoning. Stir together, lightly crushing the potatoes.
Line a medium Swiss roll-type tin with baking parchment, leaving some hanging over the sides. Tip the potatoes into the tin and flatten down. Mix the vinegar and remaining oil, drizzle over the potatoes, then bake for 40 mins until golden.