Preheat the oven to 350 degrees F (180 degrees C) and line the bottom of an 8 inch springform pan with baking powder and grease the sides of the pan.
In the bowl of a stand mixer fitted with the whisk attachment, beat egg whites together with 1/2 cup sugar on high speed until stiff peaks form, about 8 minutes. Transfer to a large bowl, set aside.
In the bowl of the stand mixer (no need to clean ifitted with the paddle attachment, combine egg yolks, remaining 1/2 cup sugar, and vanilla extract. Beat at medium speed until thick and creamy. The mixture will change color from yellow to paler color. Add egg yolk mixture to the egg white mixture and carefully fold it in with a spatula.
Combine all-purpose flour, baking powder, cornstarch, and cocoa powder. Sieve over egg mixture and fold in until combined.
Transfer to the springform pan and smooth top with a silicone spatula. Bake for 25 minutes or until a skewer interested in the center comes out clean with only a few crumbs attached.
Remove ring of springform pan and turn cake onto a parchment paper lined cake rack, peel of parchment paper from the bottom (now toand let cool completely.
When the cake is cooled completely use a serrated bread knife to cut the cake into three even layers.
To make the cherry filling, remove 4 Tbsp of cherry juice from 1 cup of cherry juice and combine it in a small bowl with the cornstarch and sugar. Bring the remaining cherry juice in a small saucepan to a simmer, remove from the heat and whisk in the cornstarch mixture. Bring back to a simmer while whisking constantly until it starts to thicken. Whisk in the cherries and remove from heat. Add about half of the kirsch to the cherries or leave it out. Let cool for 5-10 minutes.
To make the whipped cream, beat 4 cups of heavy cream (depending on your mixer you might have to whip the cream in two batchein the bowl of a stand mixer fitted with the whisk attachment at high speed until soft peaks form. Then add 1/2 cup powdered sugar and beat until stiff peaks form, about 2-3 minutes longer. The whipped cream should be very stiff and spreadable but be careful not to over-whip it. Refrigerate whipped cream until ready to assemble.
To assemble the cake, put the cake layer that was the top before on a platter. Put the springform ring (or use a cake rinaround it to make it easier to assemble the cake. Drizzle some kirsch or cherry juice over the cake, then top with half of the cherry mixture leaving a 1-inch border. Top with about 1/4 of the whipped cream, smoothing it out with a spatula.
Top with the middle cake layer and repeat drizzling with liquid, topping with cherries and cream. Put third cake layer on top (smooth side up). Set aside about ¾ cup of cream for decoration. Spread 1/3 of the remaining whipped cream on top, then remove springform ring and spread remaining cream with a spatula around the sides of the cake until completely covered in whipped cream.
Decorate sides of the cake with grated chocolate. Pipe 16 swirls of whipped cream on top and garnish middle of the cake with remaining coarse chocolate. Put a cherry on each cream swirl and refrigerate cake until serving.