To make the dressing, in a medium bowl, whisk together buttermilk, mayonnaise, sour cream, red onion, dill, parsley, garlic, lemon juice, sugar, and salt and pepper to taste (I like 1/2 teaspoon salt and 1/4 teaspoon pepper). Refrigerate at least 10 minutes to blend flavors. Whisk to recombine before serving.
On a large platter or in a shallow bowl, make a bed of lettuce. Working with one ingredient at a time, arrange in rows the chicken, blue cheese, egg, tomatoes, bacon, and avocado. Sprinkle with chives and serve with dressing.
Buttermilk: Cobb salads are typically served with red wine vinaigrette, but I love a delicious buttermilk Ranch on mine. To make your own buttermilk, whisk together 1/2 cup milk and 1 1/2 teaspoons lemon juice, then let stand for 10 minutes to curdle.
Romaine lettuce: Authentic versions of Cobb salad are made with four types of greens: romaine, iceberg, watercress, and endive. This recipe uses just romaine to keep things simple.
Eggs: To hard-boiled eggs, bring 2 cups water to a rolling boil over high heat. Place eggs in a steamer basket and lower into the saucepan. Cover, reduce heat to medium-low, and cook for 13 minutes. Fill a large bowl with ice and cold water. When eggs are done, transfer the eggs to the ice bath and cool 5 minutes.
Bacon: To fry bacon, in a cold skillet, arrange bacon in a single layer. Turn the skillet to medium heat and cook, flipping the pieces often to promote even browning, until they reach your desired doneness (8 to 15 minutes).Drain on paper towels and crumble.
Blue cheese: Roquefort is the classic choice, but any blue cheese will do. If you don't like blue cheese, substitute cheddar or Monterey Jack.
Yield: This recipe makes 1 1/2 cups ranch dressing and 8 servings of salad (3 tablespoons dressing per serving).
Storage: Any leftover ranch dressing can be stored in the refrigerator for up to 4 days. Leftover salad without dressing on it can be stored covered in the refrigerator for 1-2 days.
Make ahead: The ranch dressing can be made up to 3 days in advance. Store covered in the refrigerator. The chicken, bacon, and eggs can be prepared up to 3 day in advance, too. The vegetables can be prepped the day before and stored separately in the refrigerator (cut the avocado up right before serving to avoid oxidation).
More mix-ins: Get creative with diced green bell peppers, a can of chickpeas, poached shrimp, leftover ham, or black olives.
Chef salad: Make it a chef salad by substituting ham and turkey for the chicken and cheddar or Swiss cheese for the Roquefort.