Melt butter and add dry mustard and flour to create a paste. (refered to as a roux) Add worcestershire sauce and milk stir frequently. When sauce begins to thicken add 2 cups sharp cheddar cheese. Mix with cooked macaroni and pour into baking dish. Top with 2 cups mild cheddar cheese sprinkle with Paprika and bake at 350 degrees. Let bake for 25-30 min or until bubbley and golden brown. Allow to stand for 10 min.