1

Put the prunes into a bowl and cover with boiling water. Leave to soak for about 2 hours, or overnight.

2

Put the prunes into a saucepan with 50ml of their soaking liquid. Heat and simmer for about 10 minutes, until just a little liquid remains (about 2 tbsp). Puree with a stick blender or in a liquidizer until smooth. Cool completely.

3

Preheat the oven to 180°C / fan oven 160°C / Gas Mark 4. Spray a 20cm (8 inch) square cake tin with low fat cooking spray, then line with greaseproof paper.

4

Melt the chocolate in a heatproof bowl, positioned over a saucepan of simmering water.

5

In a mixing bowl, beat together the prunes, whole egg and muscovado sugar. Sift in the cocoa powder, flour and salt and fold in with a metal spoon. Add the melted chocolate and stir in gently.

6

In a large grease-free bowl, whip the egg whites until they hold their shape. Tip them into the chocolate mixture and fold in gently. Transfer to the prepared tin and level the surface.

7

Bake for 25-30 minutes until firm to the touch. Cool, then cut into 16 squares. Serve, dusted with a little cocoa powder.