Taking your bulb of garlic, peel the skin starting with the end opposite the stem, making sure to keep all cloves intact. Trim off the top end by about ¼ inch. Place this in an oven-safe dish, brush with the oil, and bake in the oven for about 30 minutes.
Add the chopped potatoes to a large pot. Cover with water and bring to a boil. Cook on medium heat for about 10 minutes until the potatoes are fork tender. Drain when done.
When the garlic is done, let it cool. Then squeeze out each individual clove and discard the skin. Dice the roasted garlic cloves.
In a large bowl, combine the potatoes, garlic, butter, sour cream, milk, and salt and pepper.
Mix by hand or use a hand mixer to blend. If you want them extra creamy, add more milk and keep mixing.