Rattyhatty - the BBC website gives these ingredients for a chocolate cake made with mashed potato and I discovered that each frozen disc of Aunt Bessie's mashed potato weighs 1.25 oz (which is approx 35g), so I guess you would need at least two discs for this recipe. I also understand that 5 spice powder was one of the ingredients .... I'd not put that in a sweet cake !
Chocolate Cake
Ingredients
150g self-raising flour
150g caster sugar
5 tablespoons cocoa powder
Pinch salt
75g cooked mashed potato
100g butter
2 eggs
4 tablespoons milk
Cream together the butter, sugar and mashed potato. Add the cocoa. Beat the eggs and add to the potato mixture. Fold in the flour and salt. Add the milk and mix gently. Put the mixture into two greased 8" sandwich tins. Bake at 400�F/190�C (gas mark 6) for 20 - 25 minutes. It's cooked if you spear the cake with a skewer and it comes out clean. Leave the cakes to cool, then sandwich together with whipped cream and dust with icing sugar.
(
http://www.bbc.co.uk/dna/h2g2/A533422 scroll down to very close to the bottom of the page)
I've also found another recipe for Chocolate Cake - have a peek here:-
http://www.starchefs.com/chocolate_lovers/2002 /html/may/recipe_01.shtml