Co-op Truly Irresistible Chocolate Cake

+ WHY DID I BUY? + 'Twas a Friday and I needed credit in my phone. Off I popped to the local Co-op (ooh that kinda rhymed!), but hmm... 'twas also the Boyfriend's birthday although we've both been a little cash-strapped this week so we were holding off until a week or two before buying each other presents (plus it wasn't as if we hadn't had a wee night out - we were at a gig on the Sunday. The Living End. Feckin' awesome!) but I still wanted to get my beloved a wee something. At first I considered making him cookies, then I realised that buying the stuff I didn't already have - the greaseproof paper, the eggs, the sugar... was going to be a bit ...