How can I make a roux-based cheese sauce ahead of time?

Question

I have promised to prepare several dishes ahead of time for Thanksgiving this year and most of them are well-documented on how to prepare ahead of time: bread rolls, mashed potatoes, etc. However, one item I committed to making doesn't seem to have a lot of resources dedicated to prepping ahead: mac and cheese. Some recipes exist but I do not have extreme confidence considering my prior experience with roux-based sauces.

I am planning on using this mac and cheese recipe. When the sauce & cheese are not heated to the correct temperature and then immediately put in the oven, the sauce usually comes out grainy. (Previous failed attempts resulting in grainy sauce may be the result of overheating but I have not confirmed that.) How can I go about preparing this recipe ahead of time so that it can simply be put in the oven to heat prior to serving? Since the final step is to bake it, should I just refrain from baking and instead delay until it is ready to serve? Or should I partially bake it and finish the baking later? Additionally, is there an ideal temperature the roux should be at the avoid the grainy texture?

Answer 1

The thing with mac & cheese is that it only comes up 'runny' …once.
I often make too much [intentionally] & have more the next day. The next day though, it becomes a new thing… more like cake. No more 'runny', you can cut it with a knife & it will stay standing.

The reasoning behind this is three-fold.

1. Cooked pasta alone in a dish left overnight will continue to gelatinise & clump together into one 'chunk'.
2. A roux-based sauce will also naturally set as it goes cold.
3. The pasta will pull water out of the sauce, thickening the sauce still further.

So if you prepare any part of it beforehand, you will never get back to 'runny'.
Well, maybe if you slightly under-cook the pasta & oil it; then keep it moving as it cools.

A roux itself should never be grainy. So long as you cook roughly equal weights of butter and flour for a couple of minutes before adding milk, then there is no graininess at all. For temperature, so long as the butter goes a bit frothy then it's hot enough; you'll know if you burn it, you'll smell it. You don't even need warm milk, if the flour is cooked before the milk goes in, it will work - no matter how panicky you feel when you see the first addition looks like it will never mix together, you just keep stirring until even consistency is reached. I was always taught to add the milk a bit at a time & stir to even texture before adding the next bit - but I was taught by a restaurant chef who makes it by the gallon. Home cooks tend to pour all the milk in one go [I've never dared, I know my way works].

A roux should strictly be cooked until it just starts to change colour towards brown before the milk is added. The more brown the stronger the flavour. For a cheese sauce this should be minimal, just slightly turning colour; for such as a Cajun roux, you go much darker - see SpruceEats, Traditional Cajun roux for an example.