In a large stock pot place potatoes, garlic, cold water and salt. The water should taste salty and completely cover the potatoes. Bring to a boil and cook for 30-45 minutes until a pierced potato slides easily off of the knife. Do not over cook. Drain potatoes and garlic, place on a rack and in a 250 degree oven to dry them out a bit, about 15 minutes. Transfer potatoes to a mixer with a paddle, (may have to be done in 2 batches). On medium speed, mix the potatoes smooth and add half of the cream, butter, horseradish, wasabi and season. Add the rest of the cream and check for flavor. Reserve warm.