The ratios are all wrong. First of all, if you are using low fat buttermilk, the only kind available in some areas, you will want to mix it 3:1 with plain Greek yogurt. It's the same culture, so it will act and taste like full fat buttermilk.
A better mayonnaise/sour cream/buttermilk ratio is 1:1:3. I used 0.5 cups each of mayonnaise and sour cream and added buttermilk until I liked the consistency. It took about 1.5 cups of buttermilk. I added freshly squeezed lemon juice to taste, which for me was half of a very plump lemon, and then started in on the seasoning.
The volume of dressing I made was a lot larger, so I tripled the parsley and chives, doubled the salt, onion, and garlic powders, and added a generous grind of black pepper...and a good few drops of hot sauce. A pinch of cayenne would have been better, but I had Tabasco on the counter from a different recipe. Taste as you go and remember that dry herbs will become more assertive as they rehydrate. I added a little more dill than the recipe called for, but I find dill overwhelming in most cases, so a teaspoon was plenty.
At the end, I was quite pleased, but I had to make a lot of changes.
