While I personally prefer a Cheddar Pasta with loads of vegetables cooked into the sauce, my son likes his mac & cheese closer to the modern American style.
To make this style of sauce, you need one unusual ingredient, sodium citrate, a type of salt which acts as an emulsifier. It’s available at Amazon, with $10 getting you around a pound or two, with each pound being enough for about 18 batches of sauce.
Start by putting a large pot of water on to boil, and then use it to cook a pound of pasta as usual while you make the sauce.
To make the sauce, bring 1.5 cups of water to a low simmer. For a richer sauce, use milk instead.
When the liquid is hot, whisk in 1 Tbsp of sodium citrate, about 17g.
When the sodium citrate has fully dissolved, add around 1.15 pounds of grated or sliced cheese. American cheese is the classic choice, but a mild cheddar would work, or any similar cheese such as colby, jack, or a mixture of these.
Stir the cheese gently into the liquid and wait for it to melt, then lower the heat a bit and keep it warm until the pasta is ready.
When the pasta is done, drain it and combine with the sauce, giving them a minute to meld.