Spray and line a 23 cm (9in) cake tin. I used one with a removable bottom. You could also use a square cake if you have one approx 20x20cm (approx 8 x 8 inch)
Sift the flour, cocoa powder, salt and baking soda into a bowl and set aside
In a medium bowl or the bowl of a mixer, mix the starter with the milk. Then add the oil, eggs and both sugars. If using the coffee powder dissolve in 1 tablespoon of hot water and add this to the mix. Mix with the paddle attachment till well combined.
Add the sifted dry ingredients and mix till just combined.
Pour into the sprayed and lined cake tin
Set the cake aside and heat the oven to 180 C or 350 F (leave the cake to sit during this time)
Bake for 50 minutes. The cake is ready when a skewer inserted into the middle comes out clean or with some crumbs on it. Leave in the tin to cool for 10 minutes
Once the cake is cool, you can flatten the top by cutting the dome off. Put onto a plate ready to ice
Put the butter into the bowl of a mixer with a paddle. Beat till light. Add the icing sugar and beat till light and fluffy.
Meanwhile, put the chocolate into a bowl and microwave for 1 minute until just melted. Stir well to smooth. Cool till just warm. Add the chocolate into the butter mixture and beat till light. Add the sifted cocoa powder and beat till light and fluffy
Spread the buttercream onto the chocolate cake. You can grate a some extra chocolate on the top of the buttercream
This is made with sour dough starter and it is quite a lot. It is 1 whole measuring cupful. You can collect the 200 gm of discard over several days. Make sure to feed the discard to keep it active too.