I don’t when making cauliflower cheese, but roasting cauli and broccoli defo enhances the flavour of both.
I boil/steam the cauli, make a cheese sauce, but serve them separately so we can all have as much cheese sauce as we like.
I steam the florets for about 5 mins and leave them to cool. Prefer to make my cheese sauce from scratch and always sift some Colman's mustard powder with the flour. When the sauce is made I like to whisk in an egg yolk as it gives a lovely flavour and depth. If you want to be really decadent and a touch of cream too.
I lived on my own but still make a cheese sauce from scratch (not easy working out quantities), usually have it with black pudding (not made from scratch).