Step 1Preheat oven to 180°C/160°C fan-forced. Lightly grease a 6cm-deep, 22cm round cake pan. Line base and side with baking paper.
Step 2Combine coffee and boiling water in a bowl. Stir until coffee is dissolved.
Step 3Melt butter in a large saucepan. Add brown sugar, caster sugar and coffee mixture. Stir to dissolve. Remove from heat. Whisk in eggs, milk and flour. Pour into prepared pan. Bake for 50 to 55 minutes or until a skewer inserted in the centre comes out clean. Stand in pan for 10 minutes. Turn out on to a wire rack to cool.
Step 4Meanwhile, using an electric mixer, beat cream cheese and mascarpone until smooth. Gradually add icing sugar, beating until combined.
Step 5Using a serrated knife, cut cake crossways into 3 layers. Place bottom layer on a plate. Spread with one-third of cheese mixture. Repeat with middle layer and half remaining cheese mixture. Top with remaining layer, cheese mixture and grated chocolate. Serve.