Place the water in a large stock-pot over high heat.
Quarter the potatoes and add them to the stock-pot. Cover with water by about an inch. Bring to boil and then reduce heat until the water is simmering.
Cook the potatoes about 15 – 20 minutes, until slightly soft in the middle. They should give when squeezed.
Remove from heat and drain water. Add butter, buttermilk, milk, salt and roasted garlic. Mash potatoes until creamy and the roasted garlic is well blended. I like to leave some chunks of potatoes. If you like them smooth, be careful because over mashing will result in pasty potatoes.
Add ground black pepper to taste.
