Preheat your oven to 175°C / 350°F. Spray a 12x17 inch baking tray with oil spray. Line the bottom with baking paper. Set aside.

Place a sieve over a medium mixing bowl and add the flour, cocoa powder, baking powder and salt. Sift into the mixing bowl and set aside.

Add the egg whites to a separate medium mixing bowl and mix on medium speed using an electric hand mixer (or stand mixer fitted with a whisk attachment) for about 1 minute before slowing adding 70g - 1/3 cup of the caster sugar. Continue mixing until mixture becomes thick and glossy, about 3 minutes. Set aside.

Add the egg yolks, remaining sugar and vanilla extract to a large mixing bowl and whisk on high speed for 5 minutes until pale and fluffy. Add half of the egg white mixture to the egg yolk mixture and use a spatula to fold through gently until almost completely combined. Add the remaining egg white mixture and repeat.

Sift the dry ingredients for a second time over the egg mixture. Gently fold through until well combined. Lastly, drizzle the melted an cooled butter over the cake batter and fold through until you can see no streams of shiny butter. This batter is very light.

Add the batter to the prepare baking tray and use a spatula to gently spread the mixture as evenly as you can. Bake for 10 minutes. Take out of the oven and gently run a knife around the side of the tray to help loosen the cake. Dust with about 2 tbsp of cocoa powder. Place a large piece of baking paper over the cake followed by a large chopping board. Flip the cake over onto the chopping board and take the baking tray away. Peel the baking paper away from the bottom of the cake. Tightly roll the cake starting from the narrow end. You will have baking paper rolled up with the cake. This is going to help stop the cake from sticking onto itself as it cools. Allow to cool completely at room temperature.

While the cake is cooling add the hazelnuts onto a baking tray lined with baking paper and bake on the middle rack for 10-15 minutes. Once baked allow to cool for 10 minutes before placing into a clean kitchen towel. Fold the towel over and knead the hazelnuts. This will help the skins peel off. Alternatively, you can use peeled hazelnuts and bake them for 10 minutes or until golden. Once cooled, roughly chop using a large knife.

Once the cake has completely cooled down it’s time to whip the cream. To make the whipped cream begin by adding the cream, mascarpone cheese and 1 tsp vanilla extract to a large mixing bowl. Whip to stiff peaks using an electric hand mixer. Set aside in the fridge

Add chocolate and cream into a large microwave safe bowl. Microwave for 20 seconds at a time, mixing each time until smooth. Allow to come slightly to room temperature. Alternatively, you may melt it using a double boiler. Fill a medium sized pot with 1/3 of the way with water. Bring to a boil. Place bowl with chocolate and cream over the top and gently mix until mixture is completely melted and smooth.

Slowly and gently unwrap the room temperature swiss roll. Keep the baking paper underneath as it will help us roll it back up. Spread the warm Nutella onto the cake. Add the cream and spread around evenly leaving about an inch gap on one end of the cake. Slowly and tightly roll the cake back up. Using the baking paper to do this make it a really easy process.

Carefully place the swiss roll onto a cooling rack with a baking tray underneath and drizzle the chocolate ganache on top, completely covering it. Drizzle more warm Nutella and sprinkle with remaining toasted hazelnuts.