Whisk together sour cream, buttermilk, blue cheese, onion, lime juice and ground black pepper. Cover and refrigerate for at least 1 hour before serving.
To assemble the salad, place lettuce in a large bowl and toss with 1/2 cup of the dressing. Divide lettuce evenly between six bowls and arrange remaining ingredients on top of lettuce. Drizzle additional dressing over the top and serve immediately. Enjoy!
Notes
To make a large salad to serve for a gathering or large party, double the recipe.