Add the pasta, milk, salt, and cayenne pepper (if using) to a medium-size saucepan. Turn the heat to medium then stir slowly and constantly until milk comes to a simmer — NOT a boil — 10-12 minutes. Turn the heat down to low then stir slowly and constantly until the noodles are tender, adding up to an additional 1/4 cup milk if the noodles have absorbed all the liquid but aren't tender yet. There should be a bit of milk left in the saucepan to create the cheese sauce.
Turn off the heat then add half the shredded cheese and stir until smooth. Add the remaining shredded cheese then stir until smooth. Scoop the mac and cheese into bowls then serve.
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Notes
I have used skim, 2% and whole milk for this recipe with great results.