Add the dill, parsley, lemon, garlic powder, salt and pepper. Blend.
Next add the mayonnaise, milk and yogurt.
Blend just until the ingredients are incorporated and no more. (the dressing will turn pink if blended too long)
Transfer to a sealed container and refrigerate for at least 2 hours.
Notes
I always start with 1 Tb milk and add more if needed after the dressing has refrigerated for 2 hours. The mayonnaise can be omitted for a healthier dressing. Yields 1 & 1/4 cups dressing.