Preheat your oven to 350°F (175°C). Grease two 9-inch round cake pans or line with parchment paper.

In a medium saucepan, combine unsalted butter, water, and unsweet dark cocoa powder over medium heat until smooth. Cool slightly.

In a large mixing bowl, whisk together all-purpose flour, light brown sugar, baking soda, fine grain sea salt, and optional espresso powder.

Pour the cooled butter-cocoa mixture into the bowl with the dry ingredients. Stir gently until just combined.

Add buttermilk, large eggs, and vanilla extract to the batter. Mix until smooth and creamy.

Divide batter between prepared cake pans and bake for 30-35 minutes; cool in pans for 10 minutes before transferring to wire racks.

Whip the heavy cream until stiff peaks form, then fold in semisweet chocolate chips for the mousse.

In another bowl, combine cream cheese, melted white chocolate, confectioners’ sugar, and unsalted butter until smooth.

Layer the first chocolate cake on a serving plate, adding mousse and cream cheese mixture; repeat with the second layer.

Heat remaining heavy cream, semisweet chocolate chips, and sunflower oil over low heat until smooth; cool slightly before pouring over the cake.

Pour the cooled ganache over the cake, allowing it to cascade down the sides; let set for 30 minutes.

Pipe additional frosting around the base and top with rolled cookie wafers and chocolate truffles.