Melt butter in a saucepot over medium heat. Pour half the butter over crumbs to moisten them and combine crumbs with parsley. To remaining butter, add garlic and gently cook 2 to 3 minutes stirring constantly. Add hot sauce and mustard and stir to combine then sprinkle in flour and cook 1 minute. Whisk in lemon juice, Worcestershire sauce and beer; cook beer out 30 seconds then add stock and bring to bubble. Thicken a minute more. Stir in 2 cups of cheese in figure-8 motion and season with salt and pepper to taste.
Toss pasta with Rarebit sauce and spoon into "cricks" or a casserole dish. Top with breadcrumbs and remaining sprinkle of cheese, then place on middle rack of oven and broil 2-3 minutes until bubbly and deeply brown on top.