In a blender or small food processor, combine the parsley, tarragon, dill, lemon zest and juice, anchovies, yogurt, and mayonnaise; pulse to combine. Add the garlic mixture and process until blended and smooth. Taste and season with salt and pepper. (Yield: ¾ cup. You can make the dressing up to 2 days ahead; keep covered and refrigerated. Stir before using.)