Adapted from Modernist Cuisine’s recipe for Mac ’n’ Cheese. with thanks to Linda.

  9 ounces of water
  2 teaspoons food grade sodium citrate
10 ounces of cheese, about half white cheddar and half Manchego

  Stick blender

Grate the cheese, the finer the better, and set it aside. Coarsely-grated is okay.
Bring the water and sodium citrate to a simmer (180°F) in a 2 quart saucepan.
Turn off the heat.
Add the grated cheese a handful at a time, mixing continuously with the stick blender.

Be sure each handful of cheese is blended into the liquid before adding the next handful. Adding and blending all the cheese in should take no more than a minute or two.
Use immediately or refrigerate. It’s supposed to keep for a week, but I haven’t tried.
Cleanup can be messy, and a non-stick saucepan helps.

Velveeta® is a registered trademark of the Kraft Foods company. The specks in the picture are bits of wax from the cheese. Be more careful than I was if you care about specklessness.