Preheat convection oven to 325°F or conventional oven to 350°F.
Trim broccoli and cut into ½-inch pieces
Bring water and 5 tsp salt to a boil in a large stockpot. Cook pasta for 5 minutes. Add the broccoli and cook until the pasta is slightly underdone, about 2 minutes more. Drain and transfer to a large bowl.
Warm milk in a large pot over low heat.
Whisk together fl our, the remaining 5 tsp salt, mustard, paprika and pepper in a large bowl.
Melt butter in a large stockpot over low heat. Increase heat to medium. Whisk in the fl our mixture and cook, whisking constantly, for 2 minutes. Do not brown. Slowly whisk the warm milk into the fl our mixture, whisking constantly. Cook, stirring, until the sauce is smooth and slightly thickened, about 7 minutes.
Stir in garlic powder, onion powder, Worcestershire sauce, Cheddar and Parmesan. Cook, stirring, until the cheeses are melted, about 5 minutes. Remove from the heat.
Pour the sauce over the pasta and broccoli stir to combine. Divide between two 4-inch full hotel pans. Spray underside of sheets of foil with cooking spray and tightly cover the pans.
Bake in a convection oven for 25 minutes or conventional oven for 30 minutes.
