A tasty twist on simple mashed potatoes - the sweet potato and zesty yogourt give this dish the upper hand on your festive holiday table.br br Ingredientsbr 4 unpeeled garlic clovesbr ½ teaspoon extra-virgin olive oilbr 2 medium sweet potatoes (about 1 pound total)br 2 medium russet potatoes (about 1 pound total)br 1 tablespoon unsalted butterbr 2 tablespoons coarsely chopped fresh flat-leaf parsley, plus for garnishbr 1 tablespoon finely chopped fresh sagebr 1¾ teaspoons coarse saltbr Pinch of freshly ground pepperbr ½ cup plain yogurt or sour creambr br Method:br Preheat oven to 400ºF, with racks in centre and lower thirds. Put garlic on a piece of aluminum foil; drizzle with oil. Fold to form a packet. Place garlic packet and the potatoes on centre rack; with a baking sheet on lower rack to catch any drips.br br Bake, until the potatoes are very tender when pierced with the tip of a knife, about 60 minutes. Remove from oven and let cool slightly, about 5 minutes.br br Skin the potatoes and pass through a ricer into a medium bowl. Squeeze garlic from skins into bowl with potatoes. Stir in butter, parsley, sage, salt, and pepper. Stir in yogurt, and serve.