• Preheat the oven to 350°F. Grease and line the base of a 4½-5 inch round baking tin with parchment paper.

Make the cake

• In a medium bowl, mix together the flour, sugar, cocoa powder, baking powder, baking soda, salt, and espresso if you're using it. Stir until everything is well combined.
• Create a well in the center and pour in the coffee and oil. Mix until smooth.
• Pour the batter into the prepared baking tin and gently shake to level it out.
• Bake for 25-28 minutes, or until a toothpick inserted into the center comes out clean.
• Let the cake cool in the tin for at least 10 minutes before removing it to cool completely on a wire rack.

Make the frosting

• In a bowl, combine the softened butter, powdered sugar, cocoa powder, and espresso.
• Using a hand mixer on low speed, slowly incorporate the powdered sugar. Once combined, increase the speed and beat for 3-5 minutes until the frosting becomes fluffy.

Assemble the cake

• Once the cake is fully cooled, slice it in half horizontally. If the top is domed, trim it off to make it level.
• Spread about one-fifth of the frosting on the bottom half of the cake, then place the top half back on.
• Cover the entire cake with a thin layer of frosting to seal it in, then apply a second, thicker layer, smoothing it out as you go. If desired, reserve a little frosting to pipe decorative accents later.
• Place the cake in the freezer for 15 minutes to firm up the frosting.

Make the ganache

• Finely chop the chocolate and place it in a heatproof bowl with the coconut milk.
• Heat over a pot of simmering water, stirring occasionally, until the chocolate is halfway melted. Alternatively, melt the mixture in the microwave in 10-second intervals, stirring between each one. Be careful not to overheat the chocolate.
• Stir until the chocolate is fully melted and smooth. If needed, add more coconut milk, one teaspoon at a time, until the ganache is pourable. Let it cool slightly before using.

Finish the cake

• Remove the frosted cake from the freezer and place it on a rack. Pour a small amount of ganache on top and let it sit for a few seconds, then add more until it drips down the sides.
• Place the cake in the fridge to let the ganache harden completely.
• Once the ganache is firm, you can pipe any reserved frosting on top or around the base, and dust with espresso powder or cocoa powder if desired.