Bring a large pot of salted water to a boil. Add the pasta and cook according to package instructions. Drain and reserve.
Add the butter to a medium Dutch oven and melt over medium-low heat. Whisk in the flour and keep whisking until roux is a light brown color, about 2 minutes. Slowly add the milk, whisking, until it thickens. Stir in the cheese, garlic powder, cayenne, ground mustard and some salt until cheese is melted. Fold in the broccoli and the drained pasta and stir to combine.
Sprinkle the cracker crumbs over the top. Broil, watching carefully, until golden brown on top, about 3 minutes. Sprinkle parsley on top.