Preheat the oven to 400 degrees.
Place unpeeled garlic in a terracotta garlic baker or onto a sheet of aluminum foil.
Drizzle with 1 tsp olive oil and put the lid on the baker, or wrap the garlic tightly in foil. Bake for 20-30 minutes. Set aside.
Wash, peel, and cut the potatoes into 1" cubes
Rinse with cold water, add to a 3-quart saucepan, and add cold water about an inch above the potatoes. Cover with a lid and crack it slightly. Bring to a boil and cook until tender.
Remove from heat and carefully drain potatoes.
Remove the garlic from the garlic baker or foil and gently squeeze it out of the peel into the potato mixture.
Begin mashing the potatoes and garlic together, adding buttermilk in batches by hand.
Mash until the desired consistency.
Salt and pepper to taste.