Recipe by WorkingMom2three
This is the sauce that I have been making for years. I don't usually measure the cheese, so it's just an educated guess. Put more or less as you like, but it may not thicken if you don't put enough. My original recipe called for an egg yolk to be tempered in at the end, but I find we don't need it, and then the sauce doesn't curdle. YMMV.