Preheat your oven to 375°F (190°C) and prepare a 10-inch springform pan by greasing it generously with butter or non-stick spray.

In a medium saucepan over medium heat, combine semisweet chocolate chips and butter, stirring continuously until melted and smooth.

In a large mixing bowl, whisk together granulated sugar, salt, vanilla extract, large eggs, and cocoa powder until well combined.

Pour the cooled chocolate and butter mixture into the bowl with the egg mixture, stirring gently until fully incorporated.

Pour the combined batter into your prepared springform pan and spread it evenly. Bake for 20-22 minutes.

Once baked, allow the cake to cool in the pan for about 10 minutes before transferring it to a wire rack.

Once cooled, generously spread a layer of Nutella over the cake.

In a mixing bowl, beat together cream cheese, heavy whipping cream, and sour cream until smooth and creamy.

Dissolve unflavored gelatin in cold water and let it sit for about 5 minutes until it blooms. Combine this with Nutella.

Gently fold the Nutella mixture into the cream cheese mixture until fully combined.

Pour the Nutella mousse over the Nutella-covered cake and chill in the refrigerator for at least 2-3 hours.

Prepare the Nutella buttercream by beating together softened butter, Nutella, powdered sugar, and a splash of heavy cream until smooth.

Heat heavy cream until it starts to simmer, then pour it over semisweet chocolate chips and stir to form ganache.

Spread the Nutella buttercream evenly over the mousse layer, then pour the ganache over it.

Chill the fully assembled cake in the refrigerator for several hours or overnight.

Carefully release the cake from the springform pan and place it on a serving platter. Garnish with Ferrero Rocher and serve chilled.