2cupsunsalted butter, softened at room temperature
1 1/2cupssweetened condensed milk
For Chocolate Ganache:
1/2cupsemi-sweet chocolate chips
Preheat the oven to 350F. Line and spray 3, 8-inch cake pans with parchment paper; set aside.
Prepare the sponge cake layers: place the eggs and sugar into mixer bowl and whisk on high speed for 5 to 7 minutes until light, fluffy and almost white in color. Add the vanilla and whisk to incorporate. In a separate bowl, combine the dry ingredients: flour, almond flour, baking powder and salt. Using a fine mesh sifter, add the flour into the eggs in small batches. Fold the flour in gently but thoroughly.
Divide the cake batter evenly between the 3 pans; I recommend using a kitchen scale for accuracy. Use an offset spatula to spread the batter evenly to the edges of pan. Bake in preheated oven for 13 to 15 minutes, just until top starts turning a golden color. Remove cakes from pans and set onto cooling racks to cool. Cake layers are very fragile, handle with care!
While cake layers are cooling, prepare the syrup and buttercream. For the syrup, dissolve the 2 tablespoons coffee in 1 tablespoon water, then add the simple syrup and coffee liqueur. If you prefer a cake with no alcohol, simply substitute with more simply syrup.
For the buttercream: whisk the softened butter on high speed for about 5 minutes, scraping sides of bowl often, until butter is light and fluffy. Add the sweetened condensed milk in small amounts until well incorporated. In a small bowl, dissolve the 1 tablespoon coffee in 1 tablespoon COLD water and add the coffee to the buttercream. Continue whisking for a few more minutes.
To assemble the cake: use a long serrated knife and split each cake layer in two, to have a total of 6 layers. Soak each layer generously with prepared syrup, then frost with buttercream. Repeat for all layers. Frost the top and sides of cake with remaining buttercream. Even off the tops and sides with a flat spatula, then set cake into refrigerator to set for 15 minutes.
Meanwhile, prepare the ganache: heat the 1/4 cup heavy cream in the microwave until very hot. Add the chocolate chips and stir until smooth. Transfer the ganache into a ziplock bag and let cool for a few minutes. Snip off the end of the bag with scissors, then drizzle the ganache down the sides of the cake first. Spread the remaining ganache over the top and use a flat spatula to spread it evenly.
Garnish the cake as desired. Place cake into refrigerator to set for at least a few hours, or overnight. Remove the cake from the refrigerator about 30 to 45 minutes before serving to allow the buttercream to soften.