Method

1. Preheat the oven to 160°C
2. Grease and line a 23cm round cake tin.
3. Put a medium saucepan with some water in it over a medium heat.
4. Put the chocolate, butter, salt and espresso in a medium bowl and place it over the saucepan, ensuring that the water doesn’t touch the bowl. Melt the chocolate and butter and mix well.
5. In a stand mixer, whisk the eggs and sugar on a medium–high speed for at least 10 minutes, until the mixture becomes light and creamy in colour.
6. Use a spatula to gently fold the melted chocolate mixture into the egg mixture, then very gently fold in the flour until just combined. Be careful not to overmix, or you will lose the air from the eggs.
7. Pour the mixture into the cake tin and put it on the top shelf of the oven. Bake for 30 minutes and then rotate and bake for another 8–10 minutes. There will be a few cracks on top, and when shaken gently there will be a slight wobble to the whole of the cake.
8. Cool on a wire rack for 1 hour before serving.