Keep macaroni cheese creamy after refrigerating I occasionally make Macaroni and Cheese with a béchamel/roux (and tuna, but I still call Macaroni and Cheese). I make the sauce with butter, corn flour and milk and add the cheese later. I use a lot of milk and after I've just cooked and served the dish the sauce has a beautiful creamy/liquid texture.

I cook the sauce in one pot and the pasta in another. When both are cooked I quickly drain the pasta and add both it and the drained canned tuna to the sauce. I then heat it just long enough to raise the temperature of the tuna without changing the flavour by recooking it.

However, when I refrigerate the leftovers and reheat them I just end up with clumps of pasta (and tuna) stuck together with an almost solid sauce. The flavour is still good, it's just the texture that's changed. Is the pasta absorbing extra moisture before it cools? How can I prevent this so I have creamy reheated Macaroni and Cheese?
Having made this dish again recently and experimenting with it based on the comments here can report the following:

A good creamy texture in the pot after the initial preparation will become a single hard lump in the fridge. Adding more milk before refrigeration will:


Prevent it from solidifying
Reheat (e.g. in a microwave) to a close enough texture to the original


The amount of milk that needs to be added is about the same quantity as went into the dish originally, i.e. if you used 1 litre in the dish before serving it (assuming only a small quantity removed) add another 1 litre of milk before refrigerating. If you served half of it, only add half a litre of milk, etc. The only downside is that the extra liquid separates slightly in the fridge, leaving watery pools on the surface of the food. This extra moisture can simply be stirred back into the dish before reheating.