Add roast to a large pot and cover with water. Bring to a boil over high heat and cook for two to three hours, until soft and tender. Remove to a baking dish and let cool.

Once meat has cooled, place on cutting board and slice thinly. Return to baking dish.

Preheat oven to 250 degrees Fahrenheit.

Meanwhile, prepare the sauce. In a saucepan, combine sugar, horseradish, mustard, ketchup, vinegar, and oil. Bring to a boil over high heat. Pour over roast.

Cover and bake for three to four hours.