Preheat the oven to broil. Grab the hamburger buns and spread some butter on. Pop them in the oven under broil for a minute. Then Remove them from the oven and add the roast beef. Then pop back in the oven under broil for another minute. Heat up the nacho cheese sauce and then drizzle over the roast beef.
In a sauce pan add the sauce ingredients and bring to a boil. Then remove from heat. Drizzle on the top of the bun and then the top of the nacho cheese. Then put the two sides together and eat up!