Okay, it's not my first homemade mac 'n cheese. Usually I make it with melted sliced american cheese. This is my first attempt at this recipe: Classic Mac and Cheese from Homeroom in Oakland, CA.
It calls for four cups of whole milk, a stick of butter, 1/2 cup flour, 3 cups shred sharp cheddar, and 3 oz of shredded parmesan.
I don't have whole milk in the house, so I had about 1/2 cup cream and 3/4 cup half and half, and the rest skim milk.
Later I looked it up and 4 cups of whole milk would have been 32 grams of milkfat.
A tablespoon of heavy cream has 50 grams of milkfat. So, a mere tablespoon would have MORE than enough to turn my skim milk into whole milk.
I had no idea heavy cream is that much richer than whole milk. Whoops.