Pre-heat the oven to 180 deg C/gas mark 4.
Grease and line 2 x 8 inch sandwich tins (dust them with a little cocoa powder).
Put the butter and sugar into a bowl and beat for about ten minutes, until light and creamy.
Add the flour, cocoa powder, eggs, yoghurt, vodka and vanilla and mix for a few minutes more until well combined.
Divide the mixture between the two cake tins and bake for about 25 minutes until springy to the touch.
Leave to cool while you make the vodka syrup
Heat the vodka and sugar in a small pan until the sugar has completely dissolved.
Remove the sponges from the tins and place them on a wire rack.
Brush the vodka syrup across the sponges, allowing it to soak in.
Leave to cool completely.
For the frosting
Beat together the butter and icing sugar and gradually add the vanilla extract and cream until the mixture is smooth, light and fluffy.
Sandwich the two sponges together with about half the frosting and cover the sides of the cake with the rest.
Use a puffer to blow some cocoa powder onto the sides of the cake.
Ganache - Break up the chocolate into a medium sized, heatproof bowl and set aside. Place milk and butter into a small saucepan over medium heat.
Cook 2-3 minutes, stirring occasionally, until butter has melted completely.
Increase heat to medium high and allow mixture to cook another couple of minutes, until you see tiny bubbles around the edge of the saucepan.
Do not allow the milk to boil or it will burn.
Pour hot milk into the bowl of chocolate and allow it to sit for a couple of minutes, then stir until the chocolate has completely melted and the mixture is shiny and smooth.
Pour over the cake