Combine the onion, garlic, dill, chives and parsley in a food processor or blender. If you have a small food processor I think that works best since it is a small quantity and it gets the chop just right. A blender would work but I would watch it, you want it chopped more than pureed. In a bowl combined the herbs with the sour cream, buttermilk, mayo and Worcestershire sauce. And salt and pepper to taste. I suggest using half as much pepper as salt. This dressing could be served immediately but I recommend allow to chill and stiffen in the fridge for a few hours as well as letting the flavors really marry. You won’t regret it!