Cheese sauce takes minutes to make. Cook flour in butter for a minute, pour in hot milk while stirring madly, continue to stir for a minute, add handfuls of grated cheesy goodness until melted. Salt and pepper liberally. My work here is done.

EDIT: Heat some slices of onion, a bay leaf, some black peppercorns and maybe a blade of mace in the milk while you cook the flour in the butter. Do not add them to the sauce