Chocolate Cake

1. Preheat oven to 325F(165C). Grease (3) 6” baking pans and line the base of each pan with 6” parchment paper circle cutouts.
2. Using a fine mesh sieve, sift the flour, cocoa powder, baking powder, baking soda, and salt into a large mixing bowl. Alternatively, the flour, cocoa powder, baking powder, baking soda and salt can be added to a large mixing bowl and whisked to combine.
3. In a separate medium mixing bowl, add the oil, yogurt, and sugar. Whisk to combine. Next, individually whisk in the eggs followed by the strong brewed coffee (or milk) and vanilla extract into wet batter.
4. Pour wet batter into bowl with dry ingredients and mix just until a smooth chocolate cake batter is achieved.
5. Equally divide batter into prepared baking pans and bake for 28-30 minutes or until a toothpick inserted into the center of one of the cakes comes out clean.
6. Allow chocolate cakes to cool in pans for 5 minutes before transferring to a cooling rack to cool completely to room temperature. 

Chocolate Hazelnut Buttercream 

1. Using a fine-mesh sieve, sift the powdered sugar and cocoa powder together into a large mixing bowl. Set bowl aside.
2. In the bowl of a stand mixer fitted with paddle attachment or with a hand-held electric mixer, cream the butter and salt (optional) at medium high speed until smooth and fluffy in appearance, about 3-4 minutes.
3. Add chocolate hazelnut spread into bowl with creamed butter and mix to combine, about 1 minute. Stop mixer and with a rubber spatula, scrape down the sides and base of bowl.
4. Reduce mixer speed to low and mix in sifted powdered sugar and cocoa powder into creamed butter-chocolate mixture. Once all the powdered sugar and cocoa powder has been added and incorporated into mixture, mix in the vanilla extract into chocolate hazelnut buttercream.
5. Increase mixer speed to medium high and mix chocolate hazelnut buttercream for 1-2 minutes. The resulting buttercream should thick and fluffy in appearance.

Assembly 

1. Remove the domed tops off cooled chocolate cakes with a serrated knife or cake leveler.
2. Place a clean surface on top of a turntable i.e. cake stand/cake board and spread a small amount of buttercream onto the center.
3. Add the first chocolate cake layer faced up in the center of prepared surface.
4. Spoon some of the chocolate hazelnut buttercream onto cake (about 2-3 serving spoons of buttercream) and spread into an even layer using an offset spatula. Repeat layering process once more with second chocolate cake layer and buttercream.
5. Place the final chocolate cake layer faced down on top of the second layer. This will create a flat instead of a domed cake surface once cake is completely frosted.
6. Using an offset spatula, fill in the gaps between cake layers with chocolate hazelnut buttercream and smooth out with bench scrapper. Add a small amount of chocolate hazelnut buttercream on top layer of cake — just enough to spread into a thin layer with offset spatula (about 1 serving spoon of buttercream).
7. Place cake in the refrigerator for at least 30 minutes to an hour to allow crumb coat to firm up before applying final coat of chocolate hazelnut buttercream.
8. Make chocolate ganache for drip by placing finely chopped chocolate in a small mixing bowl. Pour warmed heavy cream over chopped chocolate and allow to sit untouched for 1 minute before whisking into a smooth mixture. Set chocolate ganache aside to cool and thicken up before using.
9. Fill a large pastry bag with some of the chocolate hazelnut buttercream and cut the top 1/2” tip off.
10. Pipe chocolate hazelnut buttercream along the sides of cake until it is completely covered and spoon a good amount buttercream onto the top of cake, about 2 serving spoons.
11. Using an offset spatula, spread the buttercream on top of cake into an even layer. This will push some of the buttercream over the edge of the top layer which is fine.
12. Switch to a bench scrapper. With dominant hand, hold bench scrapper at a 45-degree angle against the side of cake and apply light pressure while rotating turntable with non-dominant hand. Repeat action until the sides of the cake is perfectly smooth.
13. Some of the chocolate hazelnut buttercream may extend over the edge of the top cake layer.  Use an offset spatula, to bring extra buttercream toward center of cake and smooth out while turning turntable with non-dominant hand.
14. Using a small spoon, drip cooled and slightly thicken chocolate ganache along the edge of cake so that it falls down the sides of cake. This will create a border around the top surface of cake. Fill that border with 1-2 spoons of the chocolate ganache and spread into an even layer with an offset spatula.
15. Top outer border of chocolate hazelnut cake with chocolate hazelnut truffles and refrigerate cake until ready to serve.