Preheat the oven to 350°F. Lightly grease two 8-inch round cake pans and line the bottoms with parchment paper.

In a medium bowl, whisk the cocoa powder and hot water until smooth and glossy. Set aside to bloom while preparing the remaining ingredients.

In a large mixing bowl, whisk together the flour, granulated sugar, brown sugar, baking soda, baking powder, and salt until fully combined.

Add the buttermilk, oil, eggs, and vanilla extract, whisking until smooth.

Pour in the bloomed cocoa mixture and whisk gently until fully incorporated. The batter will be thin.

Divide the batter evenly between the prepared pans and bake for 30–35 minutes, until a toothpick inserted into the center comes out clean. If using an instant-read thermometer, the internal temperature should register about 200°F.

Cool the cakes in the pans for 10 minutes, then turn out onto a wire rack to cool completely. Once fully cooled, wrap the layers in plastic wrap and place in zip-top bags. Freeze for easier frosting, or proceed once completely cooled.

Place the chopped chocolate in a heatproof bowl.

Heat the heavy cream in a small saucepan over medium heat until just steaming. Do not boil.

Remove from the heat and immediately stir in the espresso powder until fully dissolved.

Pour the hot cream over the chocolate. Cover and let stand for 2 minutes, then stir gently from the center outward until smooth and glossy.

Add the butter and stir until fully emulsified.

Stir in the vanilla extract and salt. The ganache should look fluid, shiny, and cohesive.

Let the ganache cool at room temperature until thickened to a spreadable consistency, about 20 minutes. For cake assembly, it should be soft but not runny, similar to warm Nutella.

If not using a cake board, place two overlapping strips of parchment on your serving plate. Place one cake layer on top.

Pipe a buttercream dam around the edge of the cake. Spoon the ganache into the center, spreading gently up to the dam without pressing down. Top with the second cake layer and chill for 15 minutes to set the filling.

To shape the heart, place a ruler or straight edge on the cake and mark a straight 5-inch line from the bottom point upward along one side. Repeat on the opposite side. Cut along the lines to remove two rounded pieces. Precision isn’t critical here, as the buttercream will hide small imperfections.

Using buttercream as glue, attach the cut pieces to form the rounded top of the heart. Chill for 15 minutes to set. Cut a small v-shape for the heart’s valley and remove.

Crumb-coat the cake and chill briefly to set the layer. Apply the final coat of buttercream, smoothing the sides and top. Add decorative piping or details as desired. Remove the parchment strips and chill briefly before slicing to ensure clean, defined layers.