Adapted from America's Test Kitchen
1/2 cup buttermilk
1/2 cup mayonnaise
6 tablespoons sour cream
1 tablespoon minced shallot
1 tablespoon minced fresh parsley
1 tablespoon minced fresh cilantro
1 garlic clove, minced
1 teaspoon fresh lemon juice
Pinch of sugar
1/2 teaspoon salt
1/4 teaspoon freshly ground black pepper
Whisk together all ingredients. Check seasoning and add more sugar, salt or pepper if needed. Store covered in refrigerator.
Makes approximately 1 1/2 cups.