Heat the oven to 180°C. Prepare a big baking tray with baking paper on it.
Whisk the egg whites at high speed. In the middle of whisking, when they start to thicken, slowly add icing sugar (a tablespoon at a time) and cornstarch.
When the egg whites are whisked, pour them on the whole size of baking paper. Make sure the top is nicely smoothened by using a rubber spatula. Sprinkle some nuts on top and then press them into the whisked egg whites. Bake for 30-35 minutes.
While the egg whites are baking, whip the heavy whipping cream in a bowl. In the middle of whipping the cream, add mascarpone - also a tablespoon at a time. When you're done, put a bowl into the fridge for a few minutes (not a necessary step).
Spread a clean kitchen cloth on the kitchen counter. Take baked egg whites out of the oven and put them on the wooden cutting board.
We need to flip the baked egg whites - to get the side with nuts on the bottom.Put a new baking paper on top of the baked egg whites, while they are still warm and on the baking tray, and flip the whole baking tray over on the kitchen cloth. Now the meringue side with nuts is on the bottom. Time to spread the Nutella over the meringue. Once the Nutella is freshly spread - take the bowl with mascarpone cream out of the fridge and add on top of the Nutella with a rubber spatula.
Now roll the roulade from the bottom to the top. Now you can see the nuts are on the outside and cream is on the inside. Once the roulade is rolled, you can use the kitchen cloth and wrap the roulade in it. Put it into the fridge for at least an hour.