In a medium-sized bowl whisk together the mayonnaise, sour cream, 1/2 cup of buttermilk and the seasonings. Whisk until smooth and creamy.
Add in the salt, pepper, and lemon juice to taste.
If needed, add more buttermilk until you reach your desired consistency.
Place in a lidded jar and refrigerate until needed. This is best if it can sit in the fridge for a few hours to allow the flavors to meld together.
Notes
Like all salad dressings, use this recipe as a guideline and then add more or less seasonings to your taste. I like mine a little heavier on the dill, of course!