Peel and finely chop the onion and garlic cloves. In a bowl, mix them with the 6 tablespoons olive oil. Add the chervil, marjoram, sage, and rosemary (all freshly chopped) to taste, and season with salt and pepper.
Cut the rack of lamb into 12 chops with several cuts on the bone to prevent them from bulging when grilling. Coat the chops with the herb marinade, place in a bowl, cover, and refrigerate overnight.
Remove the lamb chops from the marinade and drain well. Reserve the marinade for brushing.
Heat the grill to medium-high. Grill the lamb chops for 8 minutes total, turning several times and brushing with the reserved marinade.