This recipe from Nigellissima for Spinach Baked With Ricotta And Nutmeg is for two servings. Would it work for 18 servings? If so, how would you adjust the quantities and what size dish (or dishes) would you bake it in? What worries me is that in a larger quantity it will not set in the middle. Thank you.
Nigella's recipe for Spinach With Ricotta And Nutmeg is for 2 people, although if you are serving a variety of side dishes then you may find that the recipe would serve 3 to 4 people. Unfortunately scaling up the recipe to 18 people is slightly tricky as getting the centre to cook without burning the edges could be a bit of a challenge. You would probably need to bake a larger dish in a bain marie for a longer period of time and as we have not tried this method we unfortunately can't advise on timings and temperature.
However it may be worth cosidering Nigella's Spinach, Ricotta And Bulgar Wheat Pie as an alternative for a larger group. The filling is made with spinach, eggs and ricotta, plus some bulgar wheat and the advantage is that it could be assembled in advance and then baked when needed. It can also stand for longer after cooking which may be useful if catering for a large crowd. The recipe serves 8 as a main course, so could feed more if it is a side dish. Another delicious spinach dish from Nigella's repetoire is the Spinach With Pinenuts And Raisins (from Feast and on the Nigella website). This dish can be made a little in advance and then just reheated quickly when needed, and as it serves up to 8 people it should be easily doubled.