Method

1. Remove any tough stalks from the herbs, then chop them. Place half the dill and mint in a large bowl with the garlic, lemon zest and juice, oil and a little salt and plenty of ground black pepper. Mix well.
2. Make a few slashes in the chicken so that the marinade can penetrate, then add to the bowl and mix well until the chicken is well coated with the herb marinade. Cover and marinate in the fridge for at least 2 hours, longer if time allows.
3. Meanwhile, place the remaining herbs in a medium bowl. Roughly chop the radishes and cornichons then add to the herbs with the onion, mayonnaise and yogurt. Chill.
4. Cook the potatoes in boiling salted water for 15 mins or until tender. Drain, rinse in cold water and leave to cool. When cold, stir into the herb mayonnaise with seasoning to taste. Chill until required - this can be made ahead too to allow the flavours to develop.
5. When you're ready to cook, lift the chicken from the marinade and place it over hot barbecue coals or under a medium grill and cook for 20 mins, turning once. The chicken is ready when the juices run clear with no sign of pink in the centre, and the outside is nicely charred. Serve with the potato salad and a handful of rocket leaves.