one and a half Tablespoons butter
two cups milk
two Tablespoons flour
salt, pepper, and various spices (we use curry powder. mmmmm) to taste
A big hunk of grated cheese of any variety (medium-sharp cheddar is best for mac and cheese, in my humble opinion, though good results have been obtained with extra-sharp and white cheddar over here)
In a saucepan, melt the butter. Add the spices and flour and let simmer over low heat for a few minutes, stirring constantly.
Gradually add milk. Stir over low heat and allow to simmer a few more minutes.
Add cheese big heaping handfulls at a time. Stir until each addition is melted before adding more. It's "right' when it has reached your personal degree of cheesiness.
My personal degree of cheesiness usually uses a whole whomp-load of cheese.