In a sauce Pan, pour in about a cup of milk and about 1/2 a cup of flour. Whisk well.
Turn the heat on to low, and stir the concoction until it warms up and starts to thicken. Then, grate in a bunch of cheese. You don't want the milk flour mixture to be too thick when the cheese gets in, otherwise, it will be too thick. You just want the flour to promote thickness when warm, but keep the stuff relatively liquidy when cool. So, if the mixture is too thick before the cheese goes in, just add some milk and mix well.
Over low heat, stir the grated cheese milk mixture until everything is melted and it reaches the appropriate thickness. Do not boil, otherwise the mixture will become grainy.
From there, experiment.