The way I normally go about making a cheese sauce for something like macaroni cheese, I start with a roux, slowly add milk, heat to thicken then add the cheese. This works just fine and is great if the food is being eaten immediately.
Recently I've taken to batch cooking my meals for the week, so I'll cook up 7 portions of a meal and have them over the course of the week.
When I've tried to do things like macaroni cheese or a carbonara, once the meal has cooled in the fridge it becomes a solid block that's hard to serve and never really goes back to what it was when it was fresh if it's reheated.
Is there a method of creating a cheese sauce which, either doesn't solidify when it's cooled (more viscous is okay, i just don't want it to be a solid block) or at least will go back to being closer to what it was fresh, once it's been reheated?