In a large bowl, combine mayonnaise, buttermilk, sour cream, parsley, dill, salt, onion powder, garlic powder, pepper, and sugar, whisking well. Add chicken, stirring to coat. Cover, and refrigerate for 4 hours to let flavors meld.
Using a serrated knife, cut croissants in half horizontally. Fill with chicken salad.
Recipe by TeaTime Magazine at https://teatimemagazine.com/ranch-chicken-salad-croissants/