1 Preheat the oven to 400°F. Rub off excess papery skin from the garlic heads without separating cloves. Slice the tips off each head, exposing the cloves.2 Place garlic heads on a square of aluminum foil, sprinkle with 1 Tbsp. water and pinch edges of foil together to make a package.3 Roast until garlic flesh is very soft, 45 minutes to 1 hour. Unwrap garlic and let cool slightly. Meanwhile, place the potatoes in a large saucepan and cover with cold water.4 Season with 1/4 tsp. salt. Bring to a boil. Cook, covered, over medium heat until potatoes are tender, 7 to 9 minutes.5 Drain well; transfer to a large bowl. Toss gently with the vinegar and let cool. When garlic is cool enough to handle, squeeze the pulp into a food processor or blender6 Add mayonnaise, yogurt, mustard, 1/4 tsp. salt and pepper; blend until smooth. Add the dressing to the potatoes and toss to coat.7 Finely chop 3 of the hard-cooked eggs and add to the potatoes along with the celery, olives, pimientos, parsley and chopped chives (or scallion greens).8 Stir gently to mix. Season with the remaining 1/2 tsp. salt and pepper. Transfer to a serving dish and sprinkle with the paprika.