what to turn basic sponge into choc cake - how much cocoa do I add?

[katierocket]

And do I reduce flour accordingly?

Minus a couple of tablespoons of flour and add that amount of cocoa powder.

Add 3 tablespoons of cocoa mixed up with hot water and left to cool
Don't think I have ever reduced flour ...

thanks

i always replace 1oz flour with 1 oz cocoa powder