Cheese Sauce

Put all ingredients in metal bowl set over barely simmering water. Heat, whisking until cheese and butter are melted, and then stirring with a wooden spoon, until sauce is slightly thickened and registers 165 on instant-read thermometer, 5-8 min. Remove bowl from pan.

Cheese 0.25lb Italian Fontina, rind discarded and cheese coarsely grated)
Milk 0.5c
Egg Yolks 2 large
Butter 1T