Add some horseradish to a bit of cream and simmer for a while, boil up some potatos until soft and mash them with the cream/horseradish mixture, butter, salt, pepper, and garlic powder (if you want)
You have to be very careful not to get too much horseradish, and you usually want to strain that out so you just get the infused cream, but the subtle flavor of the horseradish in the mashed potatoes is amazing