- Crumble 1 cup of the blue cheese and set it aside as a garnish.
- Set up a food processor and, with the motor running, drop the chopped scallions through the feed tube. After 10 seconds, shut off the machine and scrape down the sides of the bowl.
- Add the remaining chopped blue cheese and pulse a few times to chop it further.
- Stop the motor and add the mayonnaise, vinegar, and 2 tsp. black pepper.
- With the motor running, add the buttermilk. Check the texture; if it is too thick, add more buttermilk to produce a thick and creamy, but pourable, dressing. (The dressing may be prepared up to 3 days ahead; store in an airtight container in the refrigerator.)
- To assemble the salad, lay the iceberg quartered wedges cut side up on 8 salad plates.
- Spoon about 1/4 cup of the dressing over each, then sprinkle each with some of the reserved blue cheese and a few grinds of black pepper.
- Leftover dressing will keep for 1 week in an airtight container in the refrigerator.