Preheat oven to 375 degrees. In a large bowl, combine cauliflower and potato. Drizzle with 1 Tbls. of the oil and season with salt and pepper to taste. Toss to combine. Place on a rimmed baking sheet and set aside. Cut the top of the garlic bulb to expose the cloves. Place garlic, cut side up, on a sheet of foil. Drizzle with remaining oil. Bring sides of foil together to enclose garlic. Crimp to seal. Place garlic and baking sheet with potatoes in oven. Roast 20 minutes or till softened. Let cool slightly. Cut or squeeze garlic from peel and place in a blender. Discard peel. Add 2/3's of the cauliflower mixtures to blender. Pulse several seconds. In a large bowl coarsely mash remaining cauliflower mixture with a fork. Add blended cauliflower to bowl and stir to combine. Add spread or oil and milk. Stir to combine. Season with salt and pepper to taste. Place in a serving bowl and sprinkle with cheese.