We found this recipe in Olive Magazine (UK) and used it for our daughters 6th birthday a couple of weeks ago. It's up there with the best of the best choc' cakes for eye appeal as well as flavour and we're heavily into chocolate cake, so I'm not saying that lightly . As it was mostly for a bunch of kids we decided against dusting it completely with cocoa powder, using real chocolate hundreds-and-thousands instead. but doing this could make it appropriate for say a dinner party, coffee break, breakfast lunch and supper or just as a casual snack!
Oh I forgot to mention, this chocolate cake is not overly sweet and it's ridiculously easy to bake.
What are you waiting for?

Wash your hands and pre-heat the oven to Gas Mark 3. 140C / 275F or if fan assisted 160C / 325F

Step 1: Ingredients. (metric)

For the cake mix:

250g / 9 oz. Self raising flour.
250g / 9 oz. Unrefined soft brown sugar.
50g / 2 oz. Best quality cocoa powder ( not drinking chocolate, gnargh! ) .
250g / 9 oz. Plain / Dark chocolate - again the best you can afford / liberate etc.
250g / 9 oz. Butter, unsalted is ok if you must, but a low salted (1.8%) is preferable.
4 Large eggs.

For the Ganache / icing.

400g / 14 oz. Plain / dark chocolate.
284ml - 300ml / approx 9 fl. oz. Single (thin) cream, the real stuff, accept no substitute.
25g / 1 oz.Butter ( as above ).
Cocoa powder for dusting.
2 1/2 - 3 heaped dessert spoons of icing sugar.

A sheet of baking parchment / grease-proof paper 38x38 cm / 15x15 inches approx.

Abov is the International Standards Symbol ISO 3864 denoting chocolate cake making in progress.

You can check out the real ISO 3864 it might even save your life one day.

Step 2: Line a 20cm / 8inch Square Cake Tin

This picture shows how to fold to get the uprights. If drawing on your baking sheet I'd use a pencil not a pen. Fold the sheet so that the pencil marks are on the non-cakeside? of the baking sheet.

Use the base of the cake tin for your outlines, not the top, or you will have difficulty getting it in the tin (we've all been there).

Step 3: Cutting the Baking Sheet

You should end up with this pattern of cuts , keep the four short tabs on the outside of the long tabs when placing in the tin.

Step 4: Into the Tin...

Ready for the cake mix.

Step 5: The Cake Mixture

Get your mixing bowl and favourite utensil. Put the flour, un-refined sugar and cocoa powder in and mix. In a saucepan melt the butter and chocolate with 200ml of water, when melted add it to the dry ingredients in the mixing bowl, break the eggs in too and beat it all up.

Gloop!

Pour the cake mixture into your lined cake tin and bake for one hour on the middle shelf of the oven. When the hour is up, insert a skewer into the centre of the cake, if it comes out clean it's done. If cake mix sticks to the skewer it needs a little longer, give it another 5 minutes and check again.

Step 6: Cake Done

Finished baking, carefully tip it out remove baking paper and put on a wire rack to cool completely, if you don't, the icing / ganache might slip off. It looks a bit rustic on top but that's ok, the next steps will fill / cover all the cracks.

Step 7: Ganache Ganache

Ok I've gone all lardy-da. It's called Ganache, not icing, because it's made with cream butter and chocolate not sugar+fat+egg white etc. Ganache is from the French word for "jowl" I suppose because if you eat too much they will increase in heft.
Ganache also means idiot or fool. Moving on then.

Melt the chocolate and butter on a very low heat, add the cream untill it's all smooth and then leave to cool slightly, next add enough icing sugar to stiffen the ganache, it will also turn more opaque.

Step 8: Layer Cake

Depending on your knife skills you'll either want to cut the cake horizontally for two or three layers, bare in mind the more layers the less ganache you'll have for the topping ( or just double the quantities of ganache! ). I recommend using a ham knife or one with an extra long blade at least.
Using a spatula / pallet knife spread each layer with the ganache, smooth it down as you go.

If you find small people hovering around you at this stage, they can be easily side-tracked by giving them the near-empty ganache bowl and a couple of spoons.

Step 9: What's That Loitering in the Fridge?

In conclusion: this is not the fanciest looking of cakes, but if you are the type who would trade your own grandmother for a slice of chocolate cake you have to try this recipe ( that way you get to keep the old girl too! ).

I'm presuming that the judges at 'ibles have to actually make all these cakes in the interests of unbiased scoring? (wow, what a task).

But if not then here's some gratuitous cake shots.

Enjoy :)