As instructed on the packet, cook pasta in a big pot of boiling salted water.
Melt the butter in a saucepan in the time between.
Add the flour and whisk till combined.
Pour the milk in carefully, then mix in the onion, garlic, and pepper powders. Let it simmer with the whole mixture on a low fire, stirring often, as the milk will begin to thicken.
Out of heat, stir in cheese until melted. The specific choice of cheeses has a very nice balance of acidity to bitterness without overpowering. You can easily substitute the combination to suit your taste. Taste and make any modifications that are necessary.
Add pasta to the sauce, stirring everything together perfectly.
To make a "baked" mac and cheese, transfer to a sheet of baking parchment and sprinkle 1/4 cup parmesan cheese and about 1/3 cup breadcrumbs on top. Under the broiler for three to five minutes, until the outside is golden brown. For this recipe, broiling is recommended over baking because it will crisp the top without drying out the mac and cheese and preserve its flavor!
Enjoy and serve right away!