Preheat the oven to 350 degrees F. Line 2 9" round cake pans with parchment paper and grease the bottom only.
Rub the skins off of the hazelnuts then pulse in a food processor until finely ground. In a large bowl, whisk the flour, sugar, baking powder, salt, and ground hazelnuts in the bowl.
In another bowl, whisk together the oil, water, egg, and vanilla. Fold the liquid mixture into the flour.
Meanwhile, beat the egg whites with the cream of tar tar in the bowl of your stand mixer over low for a minute, until foamy.
Slowly increase to medium high, and beat for 2 to 3 minutes until soft peaks form.
Fold the egg white mixtures in 3 batches to the flour mixture until combined.
Divide between the two prepared pans. Wiggle and tap the sides gently to remove air bubbles.
Bake the cakes for 25 to 30 minutes, until light and golden and spring back when gently pressed.
Place the pans on wire racks and cool for 15 minute. Run a knife around the edges and flip onto the cooling racks and cool completely.
For the Frosting
In the clean bowl of your stand mixer, beat the butter about 1 minute. Add the salt and cream 1 minute longer.
Scrape down the sides and add the sugar in small batches until combined.
Increase the speed to medium and cream until all combined.
Scrape down the sides and start to marshmallow creme until fluffy, about 5 minutes.
Reduce the speed, add the liqueur and beat one final time until combined.
Freeze the shredding disk to your food processor and chocolate for 20 to 30 minutes before fitting the chocolate through the feed tube and shredding.
Arrange the shredded chocolate on a sheet pan and freeze until ready to use.
Frost the Cakes
Spread 1 cup of the frosting on the first cake layer. Top with the second cake and spread the remaining frosting evenly over the top and sides of the cake.
Make a little shovel out of folded parchment and scoop up some of the chocolate flakes.
Carefully press scoopfuls of the chocolate along the sides of the cake and the top if you desire. Allow to chill in fridge until ready to serve.
When serving, allow to sit at room temperature for 20 minutes before serving.