Cooling/Resting Time: 0 minutes
Cook pasta according to package directions and reserve 1/2 cup pasta water before draining.
Melt butter in a medium saucepan over medium heat.
Whisk in flour, mustard powder, salt, and garlic powder and cook for 1 minute until golden and bubbling.
Reduce heat to medium-low and slowly add warmed milk, whisking constantly until smooth.
Cook, whisking constantly, until sauce thickens enough to coat the back of a spoon, about 3-5 minutes.
Remove from heat and add cheese gradually, 1/2 cup at a time, stirring until melted before adding more.
Pour cheese sauce over pasta and stir to combine.
Add reserved pasta water 1/4 cup at a time if sauce is too thick.
Taste and adjust salt and pepper as needed.
Serve immediately with optional smoked paprika.