Preheat the oven to 180°C.
Grease a 23cm x 33cm Swiss roll tin with sunflower oil and line with parchment.
Whisk egg yolks and sugar in a large bowl until light and pale.
Whisk in the sifted cocoa powder until combined.
Whisk egg whites in a separate bowl until stiff peaks form.
Fold egg whites into the cocoa mixture in two batches.
Pour mixture into the tin and spread evenly into the corners.
Bake for 20 minutes then cover with a dry tea towel and a damp cold tea towel for one hour.
Toast almonds and hazelnuts in a dry frying pan until golden.
Cool the nuts slightly and chop them roughly.
Caramelise the sugar in the same pan until golden-brown.
Stir the chopped nuts into the caramel.
Pour onto a lined tray to cool then break into small pieces once set.
Whisk the cream to soft peaks and fold in the caramel nut pieces.
Turn the sponge onto parchment paper dusted with cocoa powder.
Remove the lining paper and spread the cream mixture over the sponge.
Roll up the sponge from the long end using the paper for support.
Dust with additional cocoa powder and sprinkle with grated chocolate.