for about 5lb of potatos i mash as normal (a stick of butter and enough milk to make creamy) salt and pepper. for the galic part i take an entire head of garlic (large, if small i use two) and without breaking the cloves off the head i cut the head in two. (creating a top and a bottom). drizzle both cut halves with olive oil, sprinkle with a little salt and pepper and wrap in foil. bake in oven until garlic is brown. (about an hour for a large head).
squeeze that roasted garlic from it's skins and mash into your potatos. very sweet, rich (not strong or overpowering) garlic flavor. no need to chop, garlic will be mushy and spread all thru mashed spuds.
also can jazz up and use sour cream, cheese of various types.