I just made this. Do be VERY careful not to let the egg yolks go too thick - I just managed to rescue mine by using the egg white mixture to loosen it up while I was mixing in the cocoa.
I used Sainsburys cocoa powder. I actually only used half the sweetener - I only had 40g of sweetner in the house, and hadn't thought it mighn't be enough (2oz = 58g!!), so I only put in one ounce. For me that was fine, as I prefer my chocolate somewhat 'bitter'.
The cake itself was lovely. Didn't taste eggy at all, and the texture felt like a really light victoria sponge! For my next piece I'm going to have it with vanilla yogurt and strawberries - I think it will be delish!!!!
UPDATE....
Other Half, who is a chocaholic like you wouldn't believe, really loves this cake - I bet it'll all be gone by the time I get home from work tonight (he gets in 2 hours before me)!!!!