Place a pot with enough water to boil the pasta on a burner and set to high heat. Salt the water to bring to a boil faster.
Prep your cheese. I usually just cut up the blocks I am going to use so that I have 1.5 blocks at the ready. Dice the blocks up into smaller cubes. Save the other 1.5 blocks for snacks and other recipes. I crumble the American cheese right into the sauce as it is heating. I also grate the parmesan directly into the sauce when it is finished, but you can grate ahead of time, if you prefer. Nothing needs to be exact here.
Give the water a few minutes to heat up and then start the sauce. Dump the two tablespoons of the cornstarch into the pan.
Place the sauce pan on a burner and set to medium heat. SLOWLY pour in the milk, mixing well with a wooden spoon as you do this. Add the 2 tbsp butter. You are trying to avoid creating any lumps. Keep stirring the mixture and ADD THE CHEESE IN BATCHES. You can let it melt for a bit, but stir every few minutes. You want to see a bubble or two every so often, but definitely do not boil or the sauce will curdle.
Add in several big shakes of hot sauce -- this gives the sauce a nice deep color reminiscent of the blue box and lends a sublime heat to the dish :) If your family just doesn't like hot seasonings, you can skip this step.
Keep stirring until all of the cheese cubes are melted. Turn off and remove from heat . Lit sit for a minute. Add the parmesan--you can either fold in or grate the parmesan into the sauce. Save this step for last--just like making an Al Fredo sauce. It prevents the cheese from heating too long and curdling. The parmesan will melt nicely into the sauce. Cover the sauce with a lid and tend to the pasta.
Cook the pasta extra Al Dente--shorter than you would for a normal pasta. Drain the pasta well in a collander and do not rinse. Let it sit for 30 or more seconds. Transfer back into the pot. Using a wooden spoon, pour the cheese sauce over the pasta, scraping out as much as you can of the cheese sauce. You may want to use a rubber spatula to get all of it. Stir and fold several times into the pasta, but do not over stir.
That's it! You are done. Now continue prepping your meal and prepare for the compliments!