In a bowl, triple sift the AP flour, corn flour, and cocoa powder, together.
In another bowl (with a capacity of at least 2 cups), place the melted butter.
Lightly butter and line three 9 inch cake pans with parchment paper. Alternatively, just line the bottom, and butter and dust the sides with a light coating of cocoa powder.
Preheat oven to 350°F / 180°C.
Place all the eggs and sugar in your heat-proof mixer bowl (which is preferably metal) and whisk gently to combine.
Place the bowl over a pot of simmering water (make sure the water is not touching the bowl), and whisk continuously until the eggs are lukewarm, about 3-4 minutes. Remove from the heat.
Place this mixer bowl in your bench mixer and with your balloon whisk attachment - whisk the mix on medium high for 5 minutes.
Transfer about 1 ½ cups of the egg mix into the melted butter and mix the butter through the egg mix. Set aside.
Sift half of the flour mix into the whipped egg mixture and fold through gently using the same whisk attachment from the bench mixer (the balloon whisk), or a rubber spatula (I use the balloon whisk).
Now sift the other half of the flour into the whipped egg mixture as well and fold through to mix well.
Add the butter + egg mix and fold through gently. Take care not to deflate it too much (there will be some deflation after the butter mix has been added).
Pour the batter equally into the 3 pans and bake in the preheated oven for about 20-30 minutes. (You know the cake is done when you gently press down on the top of the cake in the center and it springs back up and the sides are starting to shrink away from the sides of the pans).
Leave them to cool for a few minutes and turn them out on to a wire rack to cool completely.
Combine the coffee and sugar in a small saucepan and heat until the sugar has dissolved. Simmer the mix until it reduces to about 1 1/2 cup of coffee syrup, that is sweet, but not too sweet.
While warm, brush this over the cake layers, on both sides. The layers need to be generously brushed with the coffee syrup (about ¼ cup per side - 1/2 cup per layer).
Carefully wrap the cake layers in plastic wrap and chill in the fridge until the buttercream is ready (or overnight). The cakes will be fragile, chilling it makes it easier to handle.
Coffee Caramel Buttercream Frosting
In a heavy duty saucepan, sprinkle the sugar evenly over the bottom of the pan - the thinner the layer of sugar, the easier and quicker it melts. (Please see Notes)
Heat it over medium heat, but keep an eye on the sugar AT ALL TIMES. When the edges of the sugar layer start to caramelize and turn light amber in colour, drag your spatula from the edge to the center, moving the caramelized sugar away from the bottom of the pan and replacing it with unmelted sugar. The sugar may clump up at this point, and that is OK.
Make sure the sugar DOES NOT BURN, by moving the caramelized sugar around.
If the sugar is dissolving too quickly for you, you can turn down the heat to slow down he caramelization.
All the sugar will eventually caramelize into a dark amber colour, with no clumping up.
Take the caramel off the heat and add the warm cream & salt and stir. The caramel will bubble up.
Return to low heat and stir frequently until the caramel has completely dissolved. Add the coffee granules and stir till they dissolve.
Simmer for another 6 minutes and pour the caramel into a pyrex or heatproof jug and leave it to cool completely.
Once the caramel sauce has cooled completely (to room temperature), pour this into your mixing bowl. Whisk with a whisking attachment, and add the butter while whisking. Whisk until the caramel and butter have mixed well (make sure to scrape the sides and bottom of the bowl to ensure proper mixing).
Add the Icing sugar in 3-4 batches (whipping on low speed upon addition, and increasing it slightly once incorporated). The batches make it easier to whip the buttercream, so that you don’t get a “cloud” of icing sugar when you whip.
Add the cream and whisk for a few more minutes, until you have a soft, creamy, nicely whipped frosting.
You can use this immediately, or store it in the fridge - but whip the frosting before use, and let it come to room temperature.
Place a dab of buttercream on your cake board and secure one layer of the mocha genoise on top of it (smooth base, down)
Roughly measure ¾ cup of frosting onto this layer and spread it out evenly. Place another cake layer on top (smooth base facing up this time).
Spread another ¾ cup of the frosting evenly on top.
Place the final layer on top (smooth base facing up again). Apply a thin “crumb coating” of frosting and refrigerate until the frosting sets - about 30 minutes.
Spread the rest of the frosting evenly over the cake. You can use an offset spatula to smoothen the frosting (or keep it messy - your call!).
To smoothen the frosting further, let the frosting layer set in the fridge for about an hour, and use a warm spatula to get a smooth surface.
Notes for caramelizing sugar - Please refer to this post on what to look for when caramelizing sugar using the dry method.
Recipe from The Flavor Bender by Dini Kodippili
Mocha Genoise Cake with Coffee Caramel Frosting https://www.theflavorbender.com/mocha-genoise-cake-with-coffee-caramel-frosting-first-blogging-anniversary/