Preheat your oven to 400°F.
Cut the top off the head of garlic to expose the cloves and wrap it in aluminum foil.
Roast in the oven for about 30-35 minutes, until the cloves are soft and golden.
While the garlic is roasting, place the potato chunks in a large pot and cover with cold water.
Add a generous pinch of salt and bring to a boil.
Cook the potatoes for about 15-20 minutes, or until fork-tender.
Drain the potatoes and return them to the pot.
Once the garlic is done roasting, squeeze the soft cloves out of their skins and add them to the potatoes.
Add the butter and milk.
Mash the potatoes until smooth and creamy.
Season with salt and black pepper to taste.
Serve the mashed potatoes warm, garnished with chopped chives if desired.