Finely chop the parsley, dill, and chives. Mince the garlic and very finely mince the red onion or shallot so they incorporate smoothly into the sauce.

Measure out mayonnaise, sour cream, and buttermilk so they are ready to combine.

Combine base and seasonings

Whisk base

In a medium mixing bowl, whisk together 1 cup mayonnaise and 1 cup sour cream until smooth and homogenous.

Add buttermilk

Whisk in 1 cup buttermilk a little at a time until combined. For a thicker dip, use slightly less buttermilk; for a pourable dressing, add a bit more.

Add seasonings

Stir in 1 tablespoon lemon juice (or vinegar), 1 teaspoon each dried onion powder and dried garlic powder, 3 teaspoons kosher salt, 1 teaspoon freshly ground black pepper, and 1 teaspoon sugar (if using). Mix thoroughly to dissolve salt and sugar.

Finish with herbs & taste adjustments

Fold in herbs and aromatics

Fold the chopped parsley (2 tbsp), chopped dill (1 tbsp), chopped chives (2 tbsp), minced garlic (1 clove), and minced red onion/shallot (1 tsp) into the dressed base. Mix until evenly distributed.

Adjust seasoning and consistency

Taste and adjust: add salt or pepper if needed. If you prefer a thinner dressing, whisk in additional buttermilk 1 tablespoon at a time until desired consistency is reached. If you like a hint of heat, add hot sauce or a pinch of cayenne to taste.

Rest

Cover and refrigerate for at least 1 hour (preferably 4–24 hours) to let flavors meld. Give a final stir before serving.

Storage

Store in an airtight container in the refrigerator for up to 7 days. Stir before each use; if separation occurs, whisk briefly to recombine.