This hearty, earthy skordalia, made dark with the addition of walnuts and red wine vinegar, is especially pungent. It is delicious with boiled or roasted beets.
Dampen the pita bread under the tap and squeeze dry very well in the palms of your hands.
Pound the garlic, walnuts, and a little salt in the mortar with the pestle and add the bread or hot potatoes, a few pieces at a time. Continue pounding, drizzling in the olive oil, lemon juice, and vinegar to form a thick, mealy paste. Add the remaining bread and/or potato as you go. Either serve at room temperature or chilled.