Step 1In a mixing bowl, combine the yogurt, lemon zest, sumac, chives and lemon juice and mix well. Transfer to a container with a tight-fitting lid and keep cold.
Step 1Start a batch of hard lump charcoal in a grill or barbecue, watching for all of the coals to turn red, 20 to 30 minutes.
Step 2Meanwhile, bring a pot of water to a boil. Add 1 tablespoon salt per quart of water. Add the cabbage to the water and boil for 1 minute. Immediately remove the cabbage and transfer to an ice bath to cool.
Step 3Dry off the cooled cabbage and drizzle all over with oil. Wrap the cabbage in foil and place directly in the coals, rotating every 5 minutes for 1 to 1 1/4 hours. Remove and set aside to cool for 10 minutes. Cut the cabbage into quarters and place on a platter, sprinkling the cabbage with fleur de sel. Have guests tear pieces of cabbage with their fingers, dipping the cabbage into the sauce.