Does cauliflower have to be parboiled before cauliflower cheese?
It might just be a timing decision.
Parboil it will take 20 mins in the oven. From raw, more like an hour.
Bear in mind how long it will take to heat to the centre whilst submerged in sauce compared to being boiled or steamed alone.
Some examples -

'Standard' recipe: parboil whilst making roux, add hot sauce to hot cauli, bake 20 mins.

Jamie Oliver's 'pre-cook' version: Make sauce, cool. Break raw cauli into dish, add sauce, save in fridge. On the day, 50 mins to an hour.

Gordon Ramsey: parboil cauli, cool, combine with sauce, 20 mins oven.

'Alternative': roast cauli with oil coating 20-25 mins. Add sauce, and another 20-30 mins in the oven. This one uses a well-darkened roux, so I think it's going for a much richer flavour than any 'regular' cauli cheese.


Generally, the time differences agree: Pre-cook, under 30 mins / No pre-cook, an hour (ish)
I love it when the Guardian does these 'test it every which way' experiments. I found one right on target… How to cook perfect cauliflower cheese
However, I would suggest if you're going to be doing this just the once for Christmas dinner that you don't play with the recognised timings. You don't want a dish of mush, yet you absolutely don't want crunchy cauli.
Four mins parboil (or personally I steam, maybe five mins maximum [depends on sizes &amp; whether you cross-cut the stalks, like with sprouts], centres still more than al dente at that point) &amp; adding hot to hot then 20-25 mins oven is safe… even if you have to hold dinner for unexpected last minute reasons, or have to juggle Yorkies, etc. Pulling it from the oven or even keeping it a few minutes more will not kill it.