In a small bowl, mash together the Greek yogurt, buttermilk, garlic and blue cheese, until blended but small chunks of blue cheese remain throughout the mixture.
Stir in the parsley, chives, lemon juice and salt. Add a few cracks of black pepper and stir to combine. Taste and add more salt and pepper if you'd like. Allow to rest for 30 minutes to allow flavours to blend. Store leftovers in a covered container in the fridge for up to 4 days. Stir before serving.