Grease a 15cm/6in silicone microwaveable cake mould with a little oil and line the bottom with a circle of baking paper. Mix the sugar, flour, cocoa, espresso powder, baking powder and salt in a bowl.

Equipment and preparation: You will need a silicone mould that has 6 x 7.5cm/3in wide, half sphere moulds. Melt 300g/10½oz of the dark chocolate in a bowl set over a simmering pan of water (make ...