Prep: Preheat your oven to 180°C (350°F). Spray two 8-inch cake pans with nonstick spray and line the bottoms with parchment paper.
Mix Wet Ingredients: In a large bowl, whisk the eggs, buttermilk, oil, vanilla, salt, sugar, sour cream, and sifted cocoa powder together until smooth.
Pour in Coffee: Add the hot coffee and whisk just until the batter is smooth with no flour lumps left.
Bake: Divide the batter evenly between the two pans (use a scale for accuracy). Bake for 25 to 30 minutes, or until a toothpick inserted into the center comes out clean. Let the layers cool completely in the pans on a wire rack.
Make the Whipped Ganache
Melt: Chop the dark chocolate and place it in a bowl. Heat the heavy cream in a small saucepan until it simmers, then pour it over the chocolate. Let it sit untouched for 10 minutes, then whisk until smooth.
Chill: Cover the bowl with plastic wrap, pressing it directly onto the ganache surface to prevent a skin from forming. Place in the fridge for about 1 to 2 hours, until cold and thickened.
Whip: Beat the chilled ganache with an electric mixer for 1 to 2 minutes until it lightens in color and holds soft peaks. Don't overmix, or it can turn grainy.
Make the Coconut Filling
Stir the shredded coconut, sweetened condensed milk, and heavy cream together in a bowl until fully combined.
Assemble the Cake
Set Layer & Pipe Dam: Place the first cooled cake layer on your plate. Fit a piping bag with whipped ganache and pipe a tall ring around the outer top edge of the cake. This holds the coconut filling in place.
Fill: Spread the coconut filling inside the ring and smooth it down evenly.
Frost: Top with the second cake layer. Use an offset spatula to frost the top and sides of the cake with the rest of the whipped ganache. Sprinkle extra coconut on top if you like.
Notes
Room Temperature Ingredients: Use room temperature eggs, sour cream, and buttermilk so the liquid ingredients blend smoothly without separating.
Weighing Dry Ingredients: Always weigh flour and cocoa powder with a digital kitchen scale for accurate results. If using measuring cups, fluff the flour, spoon it in, and level it off.
Hot Coffee Purpose: Hot coffee blooms the cocoa powder to deepen the chocolate flavor without adding a coffee taste. Swap with equal parts hot water or hot milk if preferred.
Ganache Handling: Do not overwhip the ganache. Stop beating as soon as it turns fluffy and holds soft peaks to avoid a grainy texture.
Piping a Ganache Border: Always pipe a thick ring of whipped ganache around the outer edge of the bottom cake layer to lock the coconut filling inside.
Storage and Serving: Store the cake in the fridge. Take it out 20 to 30 minutes before serving so the ganache softens and the sponge returns to a tender consistency.
Make Ahead Freezing: Wrap cooled unfrosted cake layers in two layers of plastic wrap and freeze for up to 2 months. Thaw at room temperature before assembling.