1Bring a large pot of salted water to a boil. Add pasta and cook 2 minutes less than package directions. Add broccoli florets to the pot in the last 2 minutes of cooking. Drain in a colander and set aside, reserving 1 cup of pasta water.
2While the pasta cooks, melt butter in a saucepan over medium heat. Whisk in flour and cook, stirring constantly, for 1 minute until it's a smooth paste.
3Slowly pour in milk while whisking to avoid lumps. Continue cooking and stirring for 5 minutes until the sauce thickens and coats the back of a spoon.
4Remove from heat and stir in shredded cheddar cheese until completely melted and smooth. Season with salt, black pepper, smoked paprika, and dry mustard powder.
5Return the drained pasta and broccoli to the pot and pour the cheese sauce over it. Fold gently to coat everything. If it feels too thick, add a splash of the reserved pasta water until you reach your preferred consistency.