Fill a large pot with water and set it to high heat. Add some salt to the water, just a few dashes'll do ya. Bring that water to a boil.
In a smaller pot, add the milk and flour and whisk it until dissolved. Just before the pot with water starts boiling, turn the heat to medium.
Add the macaroni to the boiling water and cook as directed on the package (generally somewhere around 8-10 minutes). Stir occasionally.
As the milk and flour mixture heats up, it will start to thicken. Be sure to stir it rather frequently, or it will form a skin on the top, and possibly burn, though I've yet to have that happen.
When the pasta is ready, dump it into a strainer to drain the water, then return it to the pot.
Remove the milk pot from the heat and add the cheese, stirring constantly until all the cheese is melted and has smoothed to a creamy consistency. If you don't stir it enough, it will have a grainy texture. Add your dash of salt, stir, then pour it over your pasta and stir until fully incorporated.
Serve. And devour.