Rub the garlic with the oil and wrap in a piece of aluminum foil. Roast in the oven for 30 minutes or until soft. Cool and squeeze the cloves out of the skins, then mince.
Place the chiles with a little of the adobo sauce in a blender or food processor and puree until they are smooth.
In a saucepan, cover the potatoes with cold water and bring to a boil. Reduce the heat slightly and cook for 30 minutes until they are tender. Drain the potatoes well.
Place the potatoes in a large mixing bowl along with garlic, butter, milk, and yogurt. Beat until smooth and creamy, adding more yogurt or milk if necessary. Gently stir in the chile and season with the salt and pepper.
