Boil potatoes in water until tender. While they're boiling, place 2 Tbsp. of the butter in a saute pan and saute the onion and garlic until browned. Set aside. Remove potatoes from heat when done and drain. Add the rest of the butter and mash or beat with mixers. Add the milk, the sour cream and the onion mixture, stirring or continue beating until desired consistency (careful not to overbeat). Salt and pepper to taste. Serve