Whisk 50g (2oz) cocoa powder with 100ml (3½fl oz) boiling water in a small bowl until smooth. Leave to cool for a few minutes.

Preheat the oven to 180°C/350°F/Gas 4 and line a 33 x 22cm (13 x 9in) tray bake tin with non-stick baking paper.

In a large bowl whisk the eggs, sugar and oil for 3 minutes, until smooth, using an electric whisk. Mix in the flour, bicarbonate of soda and cocoa paste. Pour into the tin and allow to settle.

Bake for 35-40 minutes until the cake is risen and a skewer inserted comes out clean. Leave for 10 minutes, then turn out onto a wire rack to cool.

To make the icing, melt the dark chocolate with the butter in a bowl over a pan of barely simmering water and stir until smooth. At the same time, mix the remaining cocoa powder, milk and syrup in a pan and heat until almost boiling. Whisk it into the chocolate mixture to make a glossy icing.

Smooth the icing over the cake, drizzle with the milk chocolate and leave to set. Cut into squares.

To serve now: Enjoy the cakes and keep any extras in an airtight container for a few days.

To freeze: Place in rigid plastic containers in a single layer or between sheets of greaseproof paper. Cover, seal and label. Use within 2 months.

To serve from the freezer: Thaw at room temperature for about 2 hours or until defrosted.