Heat oven to 400° F. Cut off the top 1/2 to 1 inch off garlic bulb to expose cloves. Wrap garlic in foil, place in baking pan and bake until soft and browned, about 45 minutes. Squeeze garlic from skins. Meanwhile, in large saucepan over high heat, bring 1 quart water to boil. Add potatoes, cover and return to boil. Reduce heat to medium-high and simmer until potatoes are very tender, about 10 minutes. Drain potatoes and return to pan. Heat milk in microwave oven until steaming, about 1 minute. Pour milk over potatoes, add roasted garlic and mash with potato masher. Season with salt and pepper to taste. Spoon onto four plates or small bowls. Make a well in the middle of each serving and fill with 1 tablespoon Kerrygold Butter. Drizzle each serving with 2 teaspoons truffle oil and sprinkle with 1 teaspoon chives.