storing sponge with buttercream top

[EyesDoMoreThanSee]

after my desperate post the other day I decided to make dd a giant cupcake. now made a test one and the sponge is beautiful, intending to slice the "bottom" and fill with strawberries and mascapone/fromage frais then cover top half with buttercream icing thinly, tiny red flowers and candles.

don't really want to be doing everything tomorrow as party is lunchtime but how much can I do tonight and where can I store it? I have tins which are supposedly airtight but after a sponge went odd a few weeks ago Im a bit suspicious.

thanks in advance!

Do you have a really big bowl you could put over it and then cover that in clingfilm? That's what I do with larger cakes especially if it's only over night. Do you have somewhere cool to store it?

I don't have anywhere cool, but seriously rethinking the buttercream. We cook with pure (dairy free) and I did a test run and the icing has left a metallic taste in my mouth, no idea why, DH said it was too sweet and so Considering doing the mascapone/fromage frais on top of cake as well?

But think I might bake it in the morning...

Thank you for advice :-)

Bake this evening, those giant cupcakes take ages to cool right through and decorate tomorrow.

I have never had an issue with pure (I bake lots of dairy free), it just needs a little extra icing sugar to firm it up. You could mix a little icing sugar with marscapone but you will need to store the cake in the fridge until serving.