Planet Earth cake...how on earth?

[Kitkatatonia]

DS has at the last minute decided he would like a 3D planet Earth cake for his birthday (bearthday?) on Sunday. I have a hemisphere cake tin but am not sure about which cake recipe to use. I'll be using fondant icing to cover it so I'm assuming a Madeira-esque cake would be the most suitable but if anyone has any tried and tested recipes to share, I'd be ever so grateful!

I'm also at a loss as to how I'll balance it on the cake board so any suggestions would be appreciated

Should also add that the picture included above is what I'm aspiring to but I'm under no illusions that my attempt will resemble it!

A madeira type cake would be best because of sturdiness
However I have found lots of different cakes, so long as you let them rest for a day before decorating are ok
What about a madeira that is marbled? Vanilla and chocolate?
I would say best way to balance is to roll some fondant pretty thick, cut out a circle with a smaller circle inside so almost a bit of a donut
Place the cake on this, may stop any rolling issues!
I would also recommend when you stick the two halves together, to put a layer of buttercream smoothly over the whole cake, set in the fridge for a bit, another layer, set, another layer. I find this achieves the smoothest base to then cover with fondant. At least if you get any fondant breakages you can make that area land!

I'm liking the sound of the marbled cake but I've only got Friday and Saturday night to pretty much do the whole cake so am a bit scared I won't have time. Loving the point about covering breakages with land - that's just the sort of tip that my bodging baking requires!

Have you got a reliable recipe waitingforegg, and if it's not too much trouble, could you point me in it's direction?

For a basic sponge recipe I would usually do 1 egg to every 50g of sugar and flour and then multiply for quantity needed
So e.g. 200g caster sugar, 200g softened butter beat until very fluffy, add the 4 eggs one at a time until fully combined, along with 1 teaspoon of vanilla (always bean or extract never flavouring), sift 200g self raising flour, mix until combined and avoid over mixing
To make this a chocolate recipe simply take out 25g of the self raising flour and replace with cocoa powder.
If you make a bowl of each recipe in the amount required and then swirl together to marvel (lightly mix)
Fill the mould as you normally would and bake. I usually bake at around 160ish and timing will depend on size of the cake. Use a cake tester or sharp knife to test.
If you want to do a madeira i've used this recipe www.bbcgoodfood.com/recipes/1940701/madeira-loaf-cake before and it was good, again just alter the ingredients amounts to suit the size of the cake.
You can stick the two halves together with a nice layer of buttercream
If you are short on time I would scale it as doing all baking and buttercream mixing on the friday, then assembly on the saturday. I find most disasters happen when i don't leave the cake to rest long enough