For the dressing: Combine the mayonnaise, sour cream, parsley, and chives in a medium bowl and stir until smooth. Finely chop the garlic, then sprinkle with a pinch of salt. Smash the garlic with the flat side of a knife until it becomes a paste, then add it to the dressing. Stir in the buttermilk, ½ teaspoon salt, and a few grinds of black pepper. Refrigerate until ready to use.
Place each lettuce wedge on a plate. Spoon some of the dressing on top, then sprinkle with the cheese and more chives. Serve the remaining dressing on the side.
