25g dark chocolate, chopped (don't use 75% chocolate, or the icing will be bitter)
1 tbsp strong black coffee
100g light soft cheese
100g 0% Greek yogurt
2 tbsp icing sugar
15g dark chocolate, chopped
Heat oven to 180C/160C fan/gas 4. Lightly butter and line the bases of 2 x 18cm sandwich tins with baking paper. Whisk the eggs and sugar until light and fluffy, about 5 mins with a tabletop mixer or 10 mins using an electric hand whisk. The mixture will have increased greatly in volume and be thick enough to leave a trail on the surface when the whisk blades are lifted.
Sift the flour, cornflour, cocoa and baking powder over the surface and fold in gently using a large metal spoon. Divide between the tins, gently spreading the mixture to the edges, then bake for 15-20 mins until the cakes are well risen, have begun to shrink away from the sides of the tins and spring back when gently pressed. Leave to cool in the tins for 5 mins, then turn out onto a rack.
To decorate, microwave the chocolate and coffee together on Medium for 20-30 secs until the chocolate has melted. Gently stir until smooth, then cool slightly. Beat the soft cheese with the yogurt and icing sugar until smooth, then spoon half the mixture into a small bowl stir in the melted chocolate and set aside. Place one cake on a serving plate and spread with the yogurt mixture. Cover with the other cake, then spread the chocolate yogurt mixture over the top.
To finish, microwave the 15g chocolate on Medium for about 20 secs until melted. Stir gently until smooth, then drizzle all over the cake.