Method

1. Butter a 19-20 cm (7 1/2-8”) cake tin generously, or line with non-stick baking parchment.

2. Break the chocolate into squares. Melt in a small bowl set over a pan of gently simmering water, making sure that the base of the bowl does not come into contact with the water. As soon as it has melted, take the bowl out of the pan. Beat in half the butter and then the egg yolks. Blend the flour with the remaining butter and stir into the chocolate mixture until completely combined.

3. Whisk the egg whites until stiff, add half the sugar and whisk again until shiny and thick. Fold in the remaining sugar. Lightly fold into the chocolate mixture and pour into the cake mould.

4. Stand in a roasting tin half filled with hot water and bake at 170C/325F/gas mark 3 for 1 1/4 hours. Remove from the oven and leave to cool. Turn out and leave to stand for at least four hours, or overnight, covered with a dry, clean tea-towel.

5. For the prunes, put all the ingredients (except the prunes) into a pan, stir and bring to the boil until the sugar has dissolved. Add prunes and simmer for 5-10 minutes until tender. Leave to cool and serve alongside the cake with a dollop of lightly whipped cream.