I did spend some time afterwards looking for a more suitable recipe. I wasn't successful as most seem to focus on the method, which is cumbersome, but not too difficult to do. Key is to have a thicker than normal cake batter, but not as thick as the one I ended up with. This is so the patterns retain their shape before baking. Also, I think it would work better if the pattern was made entirely of batter, not with chocolate like in my cake book, because it smudged when I cut the cake.
It had been my intention to make a cake for my Brother-in-law's birthday, however, when I established that the recommended 1 h 20 minutes was far from enough to bake the cake and after a further hour of baking I ended up with this:
I decided not to bring it along. Good thing my Mother-in-law had ordered a cake as well. I covered it with ganache before Lundulph and I tried it and he liked the ganache so much, he asked me to cut out the surface bits and throw away the middle. Of course when a cake has been baked for too long, it has a thick crust which tastes of burnt, but the ganache makes it sort of OK. We have dessert for a couple of days now. I also ended up with way too much ganache, so I'll either make another attempt at a leopard print cake or try making truffles.
I just feel terrible having to throw away a big lump of cake, but really it was quite inedible.