Heat a little bit of milk, throw in a little sodium citrate (I think it's like 1/2 a teaspoon per pound), stir until dissolved, cut or shred a big block of cheese up, melt that in, and you get magic cheese that tastes the same (it takes very little milk to make it work) but melts and remelts without issue. Instead of a bechamel where the oils separate out if you don't mix every 30 seconds to reheat it, you can just nuke the hell out of it in the microwave with no issue.