1Scrub the potatoes well, but don’t peel them. Cut into slices 1 cm thick, place in a large saucepan, and pour in enough cold water to just cover them. Bring to the boil then reduce heat to a simmer and cook for about 4 minutes, or just until the potatoes are tender; you don't want them to fall apart! Drain carefully through a colander, then let them dry out for at least 10 minutes.
2Meanwhile, put the herbed sour cream ingredients in a blender or food processor, season with pepper and blitz until creamy and bright green. Set aside in a small serving bowl.
3In a wide shallow dish, mix together the olive oil, garlic, rosemary and salt. Add your air-dried potato slices and leave for a few minutes to soak up some of the garlicky oil.
4Heat the flat plate of your barbecue to high. Cook your potato slices until golden—about 5-7 minutes on each side.
5Carefully transfer to a serving plate, then season with salt and pepper to taste. Serve hot, with the herbed sour cream on the side.
Tip: If you're feeling brave, you can cook the potato slices on the open grill of your barbecue for a chargrilled effect! Or you can use a chargrill pan on the stove.