Combine the starter, milk and flour in a large mixing bowl

Cover and rest at room temperature for 2-3 hours

Preheat the oven to 175ºC/350°F/Gas mark 4

Lightly grease a 23 x 33cm (9 x 13-inch) cake tin

In a separate bowl, beat together the sugar, oil, vanilla, salt, baking soda, cocoa and espresso powder - the mixture will be grainy

Add the eggs one at a time, beating well after each addition

Gently combine the chocolate mixture with the starter/flour/milk mixture, stirring until smooth. It will be gloopy at first; however, the batter will become smoother as you continue to beat gently

Pour the batter into the prepared cake tin

Bake for 30-40 minutes or until a skewer inserted into the middle comes away clean

Remove the cake from the oven and set it on a wire rack to cool while you make the icing

Sift the icing sugar into a large mixing bowl. Set it aside

In a small saucepan set over medium heat, melt the butter and add the buttermilk/yoghurt

Dissolve the espresso powder in the hot water, add to the pan, and bring the mixture just to a boil

Immediately pour the simmering liquid over the icing sugar in the bowl, and beat until smooth

Pour the warm icing over the cake. If you wait too long and the icing stiffens up, just spread it over the cake with an offset spatula

Combine the chocolate pieces, milk and golden syrup in a microwave-safe container. Microwave until the chocolate softens, then stir until smooth (a couple of 10-second bursts)

Drizzle the chocolate sauce over the icing