Separate 12 egg whites in 4 groups of 3. You will use egg whites to bake one cake layer at the time. Keep separately all yolks together.
Grind the walnuts and mix together with flour. Divide the mix into four equal parts.
Butter and than fit the bottom of 9″ springform baking pan with parchment paper.
Position a rack in lower third of the oven and preheat at 170 °C (340 °F).
Cake Layer (need 4)
In a large bowl, beat the egg whites until soft peaks form. Gradually add granulated sugar and beat until stiff, shiny peaks form. Mix in the vegetable oil.
Using silicone spatula, carefully fold in the ground walnuts into the egg whites. Use a scooping motion from the outside towards the middle of the bowl. Make sure the nuts are loose and not clumped together before you add them to the egg whites. You want to minimize folding time to avoid deflating the egg whites.
Use an offset metal spatula to spread the nut batter evenly into the baking pan.
Bake until golden brown, about 20 minutes.
Repeat the same procedure for another 3 layers. Let all 4 layers cool to the room temperature.
Chocolate Ganache Filling
Cut chocolate into a small mixing bowl.
Pour cream in a small saucepan and bring to simmer over medium heat.
Pour the hot cream over the chocolate and let it sit for about 10 minutes. Whisk it all together until is unified, smooth and shiny. Let it cool to the room temperature and than put it in the fridge for about 1 hour.
Buttercream Filling
Over a double boiler, at the medium heat, whisking constantly, heat up the mixture of egg yolks, granulated sugar and milk. It will take about 15-20 minutes until the yolk mixture thickens up. Put it aside and let it cool to the room temperature.
In a medium size mixing bowl mix together butter and granular sugar at high speed until soft and fluffy, about 5 minutes.
Add cooled off yolk mixture to the bowl and mix for another few minutes until everything is fully incorporated and smooth.
Assembling the Cake
Whip a chilled chocolate ganache for a few minutes, until light and fluffy. Divide ganache frosting into 4 equal parts and using an offset spatula evenly spread over the top of each of 4 cake layers.
Divide buttercream filling into 5 equal parts. 4 parts will be used for cake layers and 1 for the assembled cake side. Using an offset spatula evenly spread buttercream on top of the ganache filling.
Carefully stack up all the cake layers. Using an offset spatula spread the last part of buttercream filling around the cake side.
Decorate the side of the cake with ground walnuts. Pipe melted chocolate on top of the cake, creating a random pleasing pattern.
Leave the cake in the fridge for at least 24 hours. Before serving temper it to the room temperature for about 30 minutes.