Hi bitburgr

Many restaurants will cook the turkeys in batches over the previous days. They'll let them cool a bit (it's easier to thinly slice cooler poultry, it will be juicier when rested and you will get more portions per bird this way) slice and joint them and put them into foil gastronorm containers with a lightish minimum gravy and then blast refrigerate and hold them refrigerated. They have to be refrigerated within two hours of cooking for safety.

On the day, they'll then put all of them into ovens to rewarm slowly and hold to at least 165+ degrees F to ensure safe pasteurisation to kill any highly unlikely salmonella. They will be held at that temperature for at least 30 minutes before plating up. They'll be easier to fit now as they will be in gastronorm sized containers - each brimming full with no wasted space and making the most of every oven inch. 900 portions will now take much less room than 35 turkeys ...

The carcases can then be boiled with giblets and veg etc to make a starter turkey consome soup for the big day or improve the gravy.

Roast potatos can obviously be pre-preped in quantity and many restaurants cook their roast potatos or at least finish them by deep frying like chips ....... this is quick compared with roasting and very few will or can tell the difference ...... Other veg will possibly be held in steamers or bain maries or if they like them over cooked in slow below-boiling water.

Gravy is the saviour of pre-preped meats and most people wouldn't be able to tell the degree of pre-preping and be delighted with their meal.

I'm begining to sound like a kitchen porter ......

Hope your niece has a good day with lot's of happy campers .... who tip well ....