Make the roux/boil the pasta. In a 3-quart saucepan or a 12-inch high sided skillet, melt 3 tablespoons butter over medium heat. Use a whisk to stir in 2 tablespoons flour to form a loose roux.

Moving very slowly at first, and whisking constantly to not break the roux, very gradually add in 3 cups water, 2 cups milk, and 1 can evaporated milk. When you first start adding the liquid, stop every little bit to whisk it and smooth it out before adding more.

 Add in 1 pound dry elbow macaroni. Turn the heat up to medium high. Bring the mixture to a simmer, stirring every minute or so to make sure the noodles don't stick. After a few minutes, you will see slow bubbles coming up from the center of the pan (not just the edges). Turn the heat back down to medium low. Continue cooking and stirring on medium low for about 10 minutes, until the pasta is al dente. Be sure to stir every 1-2 minutes so that your pasta doesn't stick, and so the sauce remains creamy.

Do not drain! Turn your heat to low.

Meanwhile, get your cheese ready. Chop your American or Velveeta cheese into 1-inch chunks for easier melting. Shred 3-4 packed cups of sharp cheddar cheese. (I do not recommend pre-shredded cheddar because it does not melt smoothly and you will end up with slightly grainy mac and cheese. But sometimes convenience beats perfection, I get it. Do what you gotta do.)

Turn the heat to low as soon as your pasta is al dente. Add in about 1/3 of the cheese. Stir it well and make sure all the cheese melts before adding another bunch of cheese. Adding in batches ensures that the mac and cheese doesn't get lumpy or grainy.

Serve immediately. If you have to wait a period of time before serving, add in about a half cup of milk and stir it over low heat to loosen it up a bit. The mac and cheese will thicken as it cools.

Reheat leftovers in the microwave or on the stove on low. Add in a little milk and stir as it heats up, to make it creamy again.