Boil the pasta until al dente, according to package directions. Drain and rinse with cool water to stop the cooking, and return to the pan you boiled it in. Set aside. (Mix in a little butter to keep the noodles from sticking if it's going to be awhile before you make the sauce)
Preheat the oven to 375 degrees.
Over medium heat, melt the butter.
Add the flour, salt, dry mustard, pepper, and 1/8 teaspoon smoked paprika. Stir constantly over medium heat for about three minutes.
Stir in the milk.
Keeping on medium heat, whisk constantly for about 10 minutes, until the sauce thickens.
Remove from heat, and stir in 2 cups of the cheese, stirring until melted.
Pour the cheese sauce over the noodles and toss gently until all noodles are covered.
Add half the noodles to a two quart casserole dish.
Sprinkle on half the cheese.
Add the rest of the noodles.
Sprinkle on the rest of the cheese, and dust lightly with the smoked paprika.
Bake for about 25-30 minutes, until it starts getting a slightly dry and a tiny bit brown on top (here's the photo again!)
Cooking flour and butter together for precisely three minutes eliminates the raw starch flavor before milk is added. Whisking cold or cold-to-room-temperature milk into a hot roux requires continuous motion to prevent lumpy starch pockets from forming. Medium heat must be maintained for the full ten minutes while the sauce thickens; higher heat scorches dairy proteins at the bottom of the pan. Rinsing boiled pasta in cool water halts internal cooking, preventing structural collapse before the noodles enter a 375-degree oven. Starch molecules swell during the initial boil and contract upon chilling, which alters how effectively the cheese sauce clings to the tubular surfaces. Folding two cups of shredded cheddar into the off-heat sauce utilizes residual thermal energy to melt the dairy without breaking the fat emulsions. Layering half the dressed noodles with half the remaining cheese inside a two-quart casserole dish ensures internal pockets of melted fat. Baking for twenty-five to thirty minutes dehydrates the surface starches just enough to create a distinct, golden crust without drying out the interior. Smoked paprika contains volatile aromatic compounds that degrade under excessive heat, so dusting the spice sparingly over the top tier protects those flavors during baking.