Preheat the oven to 200C/400F/gas mark 6. Scrub the potatoes but don't peel them. Place in a pan and cover with cold salted water; bring up to the boil and simmer for about 8-10 minutes until tender.
Drain the potatoes and set aside to cool a little. Pour the olive oil into a roasting tray and place in the oven to heat up.
Use the base of a heavy glass to squash the potatoes until they split open. Carefully transfer them to the tray of hot oil and turn to coat. Sprinkle over the herbs, garlic cloves and some flaky sea salt and roast for 20 minutes.
Turn the potatoes over carefully and return to the oven for 20 minutes until crisp. Scatter over the parmesan and cook for another 5 minutes until melted. Scatter over the chopped chives and serve.