Preheat your fan oven to 160°C (325°F) or 175°C (350°F) if you're not using a fan oven. Grease and line with parchment paper three 6" round cake tins. Alternatively, you can use two 8" cake tins.
In a bowl of a standing mixer sift and combine flour, carob powder, cocoa powder, both sugars, salt, baking powder and cinnamon. These are your dry ingredients.
In a separate bowl, combined oil, eggs, applesauce and sour cream and whisk together. Add these wet ingredients to the dry ones and mix until it's just incorporated. At the end, add vanilla extract.
Divide the batter evenly among the 3 tins and bake for 20-25 minutes or until skewer inserted in the middle comes out with few moist crumbs. Do not overbake it.
Once they’re done, let the cakes cool for 10-15 minutes on a wire rack before removing them from the pans to cool completely. They will continue to cook in the pan, so it’s important that the skewer is not entirely clean, but it shouldn’t be wet either.
chocolate ganache filling
Place finely chopped chocolate in a bowl. Bring heavy cream and butter just barely to a simmer and pour over chopped chocolate. Cover it with a plate and leave it 1-2 minutes. Stir with a spatula until combined and smooth. Alternatively, you can do this in a microwave for 30 seconds. Cover with cling film, leave it at room temperature to thicken to a spreadable consistency before assemblying the cake.
rum buttercream frosting
In a small saucepan (I always use heavy-bottomed one to prevent burning) combine flour, sugar, powdered vanilla, salt and milk. Cook over medium-high heat, stirring constantly with a whisk until it thickens. This can take about 15 minutes. The moment you realize it’s startting to boil, cook for another 2-3 minutes.
Once it's done, transfer it to a bowl, put a cling film over it touching the surface to prevent "skin" forming and let it cool to room temperature. This is your pudding base. You can do this in a fridge, but before using it let it come to room temperature.
Using a stand mixer fitted with the paddle attachment, beat the butter for 5 minutes until it's pale and fluffy. Then add spoonful by spoonful of previously made pudding. Mix until it's all nicely incorporated and with no lumps. Add rum and beat for another 30 seconds until everything is incorporated. Make sure not to add too much rum, otherwise your buttercream might split.
Using a cake leveler or a long serrated knife level the tops of your cakes if needed.
In the middle of your cake board or a serving plate put some buttercream to stop the cake from moving around.
Place one cake layer on a cake board or a serving plate. Using a small offset palette knife or a piping bag, spread the frosting over the cake and make a buttercream dam/border. Fill it with chocolate ganache filling, but be careful not to overfill it, otherwise it will seep out on the sides. Top it with the next cake layer and repeat the process.
Place final layer on top, upside down, and do a crumb coat on the cake. Since we're leaving the cake half-naked, make sure to crumb coat the cake as neatly as possible. When you're done, place the cake in the fridge for at least 30 minutes before pouring chocolate drip.
If you don’t have a stand mixer, you can use a hand mixer.
Not all ovens are the same. I suggest to check the cakes at 18 min mark and then adjust the baking time accordingly. Get to know your oven!
If you still don’t own one, I advise you to buy a kitchen scale – they’re cheap and easy to use, and always guarantee the same results in baking!
Cake is best eaten at room temperature. You can keep it in a fridge, wrapped in cling film, but take it out of it at least half an hour before serving.
If you want to make a three layer 8 inch (20 cm) or 2 layer 9 inch (23 cm) cake, then double the recipe. You can do that by moving the serving slider to 24. For three layer 9 inch (23 cm) cake, triple the recipe.
If you want to know how to make meringue kisses on top, check out this recipe.