The easiest gooey chocolate cake

This cake is covered in ganache, but don't let this put you off.  It also has a weird method and some strange ingredients, again, don't let this put you off.  My daughter (aged nine) made this with very little help from me, and my help was probably more along the "interfering mother" lines than help that was actually required.
If you are looking at the recipe and thinking "I haven't got this" or "I haven't got that" then let me help you out.
Firstly, if you're like me, you never have fresh buttermilk in the fridge.  You may have once thought "I'll buy some buttermilk because I need it for a recipe" and then never got round to making the recipe so the buttermilk is sitting in your freezer.  If, like me, once you've decided to make something you need to make it immediately, then you won't want to wait for the buttermilk to defrost.  Fear not because you can make your own buttermilk (sort of).  Take half a cup of milk (skimmed or semi-skimmed) and add a couple of teaspoons of lemon juice.  Leave for a couple of minutes and the disgusting resultant gloop will serve as a replacement for buttermilk.
Ganache requires double cream.  I usually have cream stored in my freezer as a result of over-estimating the family's desire for heart-attack inducing food.  If you take the cream out of the freezer when you start making the recipe, it should be usable by the time you get to the ganache bit.  It won't look usable (it'll look like a solid lump of lard) but when scooped out into a bowl and given a jolly good stir then it will resemble something usable.  This is what I did when I made the cake.
Lastly, the cake tin needed for this is a deep (and I mean deep, sort of 10cm deep) loose bottomed or springform tin.  Whilst I do have such a tin, I don't like having to buy a new tin for every new recipe I want to try.  Other people have made this cake by splitting the mixture into two shallower Victoria sponge tins and cooking for less time.  I would guess the cooking time should be 50mins to an hour but the skewer test is your friend here.  The two cake tin method also eliminates the tricky slicing the cake in two (or three) part of the recipe.  Alternatively you can cook in a slightly bigger, deep tin if you have one, you will just need to watch the cooking time.
This is an easy cake, but not a quick cake, to make.  Don't start making it at 10pm as a treat for the next day.  The resultant lack of sleep will reduce its appeal.
Ingredients

• 200g dark chocolate
• 200g unsalted butter
• 1 tbsp instant coffee granules
• 85g self-raising flour
• 85g plain flour
• 1⁄4 tsp bicarbonate of soda
• 200g light muscovado sugar
• 200g golden caster sugar (I used white granulated and other people have reduced this to 100g successfully)
• 25g cocoa powder
• 3 medium eggs (I used large)
• 5 tbsp buttermilk (see hint above if you don't have any)

and for the ganache:

• 200g dark chocolate
• 284ml carton double cream
• 2 tbsp golden caster sugar (I forgot to add this and didn't notice the difference)

Method

• Butter a 20cm round cake tin (at least 7.5cm deep unless you're going to use two tins) and line and butter the base.
• Preheat the oven to 140C (fan oven).
• Break 200g dark chocolate in pieces into a medium, heavy-based pan. Cut 200g butter into pieces and tip in with the chocolate, then mix 1 tbsp instant coffee granules into 125ml cold water and pour into the pan. Warm through over a low heat just until everything is melted - don't overheat.
• While the chocolate is melting, mix 85g self-raising flour, 85g plain flour, ¼ bicarbonate of soda, 200g light muscovado sugar, 200g golden caster sugar and 25g cocoa powder in a big bowl to get rid of any lumps. To save time you could sieve ingredients as you add them to the bowl, or you could try a low speed in a mixer to eliminate lumps.  I just bashed the lumps with a spoon.
• Beat 3 medium eggs in a bowl and stir in 5 tbsp buttermilk or 5 tbsp of the lemon juice and milk concoction.
• Now pour the melted chocolate mixture and the egg mixture into the flour mixture, stirring just until everything is well blended and you have a smooth, quite runny consistency. Pour this into the tin and bake for 1 hour 25- 1 hour 30 minutes - if you push a skewer in the centre it should come out clean and the top should feel firm (don't worry if it cracks a bit). Leave to cool in the tin (don't worry if it dips slightly), then turn out onto a wire rack to cool completely.
• I would recommend making the ganache while the cake is cooking and you'll still have time to do the washing up and have a cup of tea.
• To make the ganache: chop 200g dark chocolate into small pieces and tip into a bowl. Pour a 284ml of double cream into a pan, add 2 tbsp golden caster sugar, and heat until it is about to boil.  Don't let it boil.  Take off the heat and pour it over the chocolate.  Stir until the chocolate has melted and the mixture is smooth.  Leave, uncovered, on the side.
• Ganache is easier to work if it isn't very runny and allowing it to cool will make life easier.  If the ganache is too stiff when you need it then quick ten second microwave blasts can get it to the right consistency.
• When the cake is cool, and hopefully the ganache is workable, then slice your cake.  I turned my cake upside-down so that it had a nice flat top and I used a very sharp long-bladed knife to gingerly slice my cake in two.  If you are feeling brave then slice into three.
• Using a palette knife use the ganache to sandwich your slices together.
• Pour the remaining ganache onto the top of the cake trying to get even coverage and allow it to cascade down the sides.  If the ganache isn't too runny it should be possible to spread it carefully over the top and around the sides.  If the ganache ends up dribbling down to the plate then use the palette knife to scoop it up and onto the sides.  Once you've finished this it should look a bit like this.

I've read that a good ganache is shiny.  Well this was shiny before it went into the fridge.  The plate looks remarkably clear of dribbly chocolate.  You know that trick that chefs do when they wipe plates with a tea towel?  I used kitchen towel to achieve a neat effect but if I hadn't scooped the ganache up back onto the cake I might have left it au naturel.
If you plan to decorate with grated chocolate curls or something that needs a sticky base then add it now.  If you want to add writing then read on.
Mix icing sugar and milk until you have a gloopy, smooth consistency; not entirely liquid but not stiff and solid.  Pop into icing bag with very thin round nozzle.  (The best icing bags are plastic bags with the corner cut off.)
Practise writing on a chopping board and then get creative.  I should have made my icing less liquid and could have used a finer nozzle, although a significant increase in artistic ability would probably have made the biggest improvement.
This is my finished result: