Place the same pan you used to cook your pasta back on the stove. Turn it on medium heat.
Place the butter in the pan and wait for it to melt.
Once, butter is melted, add the 2 tbsp of flour and 1/2 tsp ground mustard to the pot.
Whisk for 1-2 minutes until a paste forms.
Slowly pour in the warm milk while whisking constantly.
Keep whisking until milk starts to boil and thicken to a heavy cream consistency.
Once the milk mixture is thickened, turn off the heat.
When the mixture stops boiling, add in your 8oz of shredded cheese, salt, sugar, and pepper.
Stir until cheese is melted.
Add back in your pasta and mix into the cheese sauce.
Pour your pasta into a baking dish and set aside.