Line a large Swiss roll tray (13 x 9 ½ inches) with parchment paper ensuring that both the base and the sides are covered.
Put the egg whites into a large, spotlessly clean, mixing bowl and beat rapidly until the mixture forms stiff peaks. (A little lemon juice (4/5 drops) added to the egg whites tend to break them down a little better and gives you a fluffier meringue). You can use an electric hand whisk or a food mixer for this process.
When the mixture has formed peaks add in the sugar gradually, whisking thoroughly between each addition. When the correct consistency is achieved the mixture should be glossy and stiff. When the mixture is sufficiently whisked gently fold in the chopped chocolate.
Spread the mixture onto the prepared baking sheet and sprinkle with the chopped hazelnuts. Preheat the oven to 150°C/300°F/Gas Mark 2. Bake for 20 minutes until lightly browned. Allow it to cool in the tin.
To make the filling: Turn out onto a large piece of parchment facing the side with the toasted hazelnuts down. Put 3floz/75ml cream into a saucepan and bring it to the boil. Pour the boiling cream onto the chopped chocolate and mix well. Allow it to cool.
To assemble the roulade: When the chocolate ganache is cool spread it over the roulade and then top with a layer of freshly whipped cream and roll up in one fast action. Transfer to the serving platter and drizzle with melted dark and white chocolate. Watch it disappear!!