Preheat the oven to 340 F (170 C). Separate 6 eggs into yolks and whites, separated into 4 bowls: 3 egg yolks, 3 egg yolks, 3 egg whites, and 3 egg whites. Let them come to room temperature. Line two 9" round cake pans with parchment paper. If you have cake strips, soak two cake strips in water and place it around the pans. Prepare ⅔ cup of strong hot coffee, separated into two equal portions of ⅓ cup each. Add in ¼ cup of cocoa powder into one of the ⅓ cup portions of coffee, mix well and let it cool. Leave the other ⅓ cup portion of coffee as it is.

In one large bowl, sift together ¾ cup cake flour, 1 tsp baking soda, ¼ cup granulated sugar, and ½ tsp of salt. Add in 3 room temperature egg yolks, ⅓ cup of canola or vegetable oil, 1 tsp of vanilla extract, ½ tsp finely grated orange zest, and the prepared coffee/chocolate mixture. Beat with an electric mixer or by hand just until smooth and well blended. This is the chocolate cake mixture.

In another bowl, sift together ¾ cup cake flour, 1 ½ tsp baking powder, ¼ cup granulated sugar, ½ tsp of salt, and ¾ tsp of espresso powder. Whisk to combine. Then add in the remaining 3 room temperature egg yolks, ¼ cup vegetable oil, the second ⅓ cup potion of prepared room temperature coffee, and 1 tsp of vanilla extract. Beat with an electric mixer or by hand just until smooth and well blended. This is the mocha cake mixture.

In the bowl of your stand-mixer, with the whisk attachment, beat 3 room temperature egg whites and ½ tsp cream of tartar on high speed until frothy. Very slowly add in ⅓ cup granulated sugar, and beat until glossy stiff peaks are formed. Gradually and very gently fold in this meringue into the chocolate cake mixture until very well combined. Pour this chocolate batter into one of the prepared round cake pans.

Wash and dry the bowl of the stand-mixer, and repeat with the remaining 3 room temperature egg whites and ½ tsp of cream of tartar. Like before, with the whisk attachment, beat on high speed until frothy. Then very slowly add in ⅓ cup of granulated sugar, and beat until glossy stiff peaks are formed. Gradually and very gently fold this meringue mixture into the mocha cake mixture until very well combined. Pour this mocha batter into the second prepared round cake pan.

Bake these cakes in your preheated oven at 340 F (170 C) for about 35 to 40 minutes or until the cake springs back when touched lightly at the center. Let the cakes rest in the pans for 5 minutes to cool a bit. If the cakes haven't shrunk away and detached from the sides of the pan after 5 minutes, run a sharp knife along the edges to unstick them. Then invert the round cake pans onto metal racks, lift off the pans, and peel off the parchment paper the cakes were baked with. Let your chocolate and mocha chiffon cakes cool completely to room temperature on the metal racks.

Put the clean bowl of your stand mixer and whisk attachment in the freezer for 15 minutes before using them. Into the cold bowl of the stand mixer, add 2 cups of very cold heavy cream, ½ cup of powdered sugar, 1 tbsp of cornstarch, 2 tsp of vanilla extract, and ½ tsp of espresso powder. With the whisk attachment, beat at medium-high speed until stiff peaks form. Store in the fridge till you're ready to use it.

In a microwave-safe bowl, add in ¾ cup of heavy cream and microwave for 1 minute and 30 seconds, till the heavy cream is steaming. Take a metal bowl and add in 1 ½ cups of milk chocolate chips. Pour the hot heavy cream over the milk chocolate chips. Make sure all the chocolate chips are submerged in the hot heavy cream, and let it stand for 1 minute, then gently whisk until the chocolate chips are completely melted and there are no lumps. Prepare an ice bath and place the metal bowl with the milk chocolate ganache over the ice bath and continue stirring till the chocolate ganache cools enough so that it reaches a nice spreadable consistency.

Place a cake board that's larger than 9" on a revolving cake stand. Place the chocolate chiffon round on the cake board. Spread about half of the coffee cream filling mixture on top, creating an even and flat layer as much as possible, about ½" thick layer of cream. Place the mocha chiffon layer on top.

Take the milk chocolate ganache and fill in the edge of the gap between the 2 chiffon layers so that it forms a barrier between the sides of the cake and the white coffee cream filling. Once there's a barrier of chocolate sealing in the white-colored coffee cream filling, spread the milk chocolate ganache on the sides and cover up the sides of the cake completely with chocolate ganache. If you have an icing comb, create a pattern around the sides of the cake by revolving the cake stand. Clean up excess frosting at the base as needed. Spread the remaining half of coffee cream filling on top creating an even and smooth layer on the top surface of the cake.

Let this cake rest in the fridge overnight for the layers to set. After the layers have set overnight, you can create a pattern on the top surface. Cut out a shape of a leaf, or any shape you like, from a piece of parchment paper. Make sure to create little handles that fold up on the two ends of the parchment paper, so it is easy to lift it off later. This is to decorate the top of the cake. Place this parchment paper shape on top of the cake. Sift 1 tbsp of Dutch process cocoa powder to dust the top surface of the cake. Using the two "handles" on the ends of the parchment paper, lift off the parchment paper shape to reveal the white coffee cream underneath, being careful that the cocoa powder on the parchment paper doesn't fall back and ruin the decorative shape.

Store in the fridge till ready to serve. Because the coffee cream filling is on the softer side and the chocolate ganache is on the denser side, we recommend slicing the cake with a hot knife for neater-looking slices. Dip a metal knife in hot water and wipe it dry before each slice. Enjoy!