In a food processor combine 120 millilitres oil with the onion, garlic, anchovies, parsley, rosemary, 1 teaspoon of salt and 1 teaspoon of pepper. Process until the onion is finely chopped. Pour into a large bowl, add the wine and whisk well.
Related Grill Skills
Place each chicken, breast-side down, on a cutting board. Using poultry shears, cut along each side of the backbone and discard it. Open each chicken like a book. Split each chicken in half by cutting right along one side of the breastbone. Remove and discard the wing tips. Put the chicken halves in two large, resealable plastic bags. Divide the marinade among the bags. Press the air out of the bags and seal tightly. Turn the bags to distribute the marinade, place in a large bowl and refrigerate for 24 hours, turning occasionally (the meat and skin will be red in places from the wine).
Prepare the grill for indirect cooking over medium heat (180°C to 230°C).
Remove the chicken halves from the bags and discard the marinade. Pat the chicken dry with paper towels, brush all over with oil and season with ½ teaspoon of salt and ¼ teaspoon of pepper.
Brush the cooking grates clean. Grill the chicken, skin-side up, over indirect medium heat, with the lid closed, for 40 to 50 minutes. For crispier skin, turn and move over direct heat for the last 5 to 10 minutes (watch for flare-ups). Remove from the grill and let rest for about 5 minutes before cutting into serving pieces. Serve warm.