Whisk 1 small garlic clove, finely grated, ½ cup buttermilk, ½ cup mayonnaise, 2 Tbsp. finely chopped chives, 2 Tbsp. finely chopped dill, 2 Tbsp. finely chopped parsley, 2 tsp. granulated onion, and ½ tsp. mustard powder in a medium bowl until well combined.
Season with kosher salt and freshly ground black pepper.
Dressing can be made 1 week ahead. Transfer to an airtight container and chill.
