birthday cake for 25 children help!

[shufflebum]

DS2 has his party tomorrow, somehow got close to 25 children coming eek!
Can anyone give me a fail safe recipe for a large rectangular slab cake that will rise enough that I don't have to cook 2 and layer them. It's going to be a minion cake so hopefully not too tricky to decorate....
Oh and cake needs to be chocolate and dairy free, I can substitute his butter simply enough but lots of receives have yoghurt and buttermilk which won't work so well with substitutes.

Use vitalite and make a normal sponge mixture. You can use vitalite for butter icing too but obviously don't add the usual spoon full of milk. As for size I would use 16oz flour,butter,sugar and 8 eggs.

Wow, that's a lot of ingredients! My tin is a roasting tin 13x10 inches roughly, do you think that is big enough?
Thanks

Sorry, is that chocolate free and dairy free, or do you want to make a dairy free cholocate cake?

Cholocate? Is that a word?

I wouldn't worry as they never ever eat the cake. They like the idea of eating it and they might lick the icing off but that's it.

Haha, I worded that badly, cake needs to be chocolate flavour but with no milk containing ingredients!

Just remember that they only have a sliver anyway and your tin will have to be big Enough!

Great! To make it chocolatey, how much cocoa do I need to add?

I'd Google recipes for cholocate traybakes. Substitute vitality or 'Pure' sunflower spread for the dairy part.

I am liking the new word, Sanity.

To make it chocolate, a quarter of the flour with cocoa. If the mix comes out too dry you can add a little splash of warm water

This recipe ticks the right boxes. Just use a dairy free spread instead of butter. I have successfully made cakes with block Stork which is dairy free unlike the stuff in tubs.

Okay so 12oz flour and 4oz of cocoa.
I have looked at traybakes but in the past they have been very squishy and although delicious have been tricky to use with roll out icing as they get squashed!
I was considering that recipe bunbaker so I didn't have to go out to get more eggs as only got 6.
Do you think this one would be any good?
allrecipes.co.uk/recipe/24281/super-easy-roasting-tray-marble-cake-.aspx?o_ln=RecViewed_Link_1&o_is=RecentlyViewed

If you're wanting to ice it you're better with a madeira sponge it's much denser. You'll definitely need more than 6 eggs though
For that size I'd say 12 eggs, 600g each of Sugar spread and flour (or 150g cocoa 450 flour for choc cake) it's a lovely moist cake keeps for about a week. Have a look on youtube for crumbcoating a cake to get your icing smooth

Sorry just looked through that recipe, it looks great. Go for that if it means You don't need to go out

Thank you all for all your help, getting my apron on now!