In a small bowl, combine All-Purpose Flour (1/4 cup), Salt (1 teaspoon), Dry Mustard (1/2 teaspoon), Paprika (1/2 teaspoon), and Ground Black Pepper (1/4 teaspoon). Mix well with a fork and set aside.
Measure out Milk (2 cup) and grate the Cheddar Cheese (8 ounce). Set aside.
Add Unsalted Butter (1/4 cup) to a large skillet or frying pan and heat over medium-low. While the butter melts, begin heating a large pot of water to a boil for the pasta.
Once butter has melted, add the flour mixture to the butter. Use a roux whisk or a large fork to mix, whisking constantly. The mixture will begin to smooth out. Once it has cooked for about 3 minutes, slowly add the milk.
When the water begins to boil, add the Elbow Macaroni (1 pound) and cook to al dente.
Once all of the milk has been added to the roux, increase the heat slightly to just below medium. Whisking constantly, the mixture will begin to thicken to a consistency closer to cream than to milk.
When the pasta is cooked to al dente, drain into a colander but do not rinse. The starch from the cooking water will help the cheese sauce to stick to the noodles. Return noodles to the pot and cover until the cheese sauce is ready.
Turn off the heat under the sauce mixture and add the cheese. Whisk for another minute or two until cheese has melted completely and the sauce is smooth.
Pour over the drained noodles and mix well. Serve immediately.