Method

1| Preheat oven to 200°C. Line a 26 x 38cm slice tin with baking paper, with 2cm overhanging on long sides.

2| Put egg yolks and sugar in a large bowl and beat, using an electric mixer, until pale and mousse-like. Put chocolate, water and coffee in a large heavy based frying pan over a low heat. Cook until chocolate is melted. Stir in yolk mixture and set aside.

3| Put eggwhites in a clean bowl and whisk, using an electric mixer, until stiff but not dry. Using a metal spoon, fold a little of the eggwhite into chocolate mixture until thoroughly combined (this will loosen the mixture). Gently fold in remaining eggwhite and spread mixture evenly into prepared tin.

4| Bake for 12 minutes or until slightly browned and firm to touch.

5| Lift out cake using paper and put on a wire rack. Cover immediately with a damp, clean tea towel (this prevents cake from cracking) and leave to cool for at least 4 hours, preferably overnight.

6| Evenly spread ½ the cream over 1 side of cake and top with ¾ of the blueberries and ½ the hazelnuts.

7| Using paper as a guide, roll up cake, removing paper as you go. Transfer to a serving plate. Decorate with remaining whipped cream, blueberries, and hazelnuts. Dust with lavender flowers, if you like, and grated chocolate to serve.