|In a tall working glass or equivalent, add the mayo, yogurt, vinegar, and blue cheese. Combine with an immersion blender (see notes). We like to let this chill for a bit before we use it to give the flavors and texture a chance to develop, but it can also be used right away if needed.|
|Combine the celery, radish, and scallions in a bowl.|
|Slice the iceberg lettuce into 3/4"-inch rounds, one per serving. Transfer each to salad plates, then spoon dressing onto each serving.|
|Top each iceberg round with an even portion of the celery mixture, then top with crumbled blue cheese, fleur de sel, and pepper. Serve.|
source: Ina Garten's Make It Ahead
For making the dressing, the original recipe calls for a food processor, but we make our dressing with an immersion blender just to make clean up easier.