Preheat your oven to 350°F (175°C) and prepare two 9-inch round cake pans by greasing with butter and dusting with flour.

In a medium saucepan over medium heat, combine unsalted butter, water, and unsweet dark cocoa powder. Stir continuously for about 3–5 minutes until melted and glossy.

In a large bowl, whisk together all-purpose flour, light brown sugar, baking soda, fine sea salt, and espresso powder until fully combined.

Gently fold the cooled chocolate mixture into the dry ingredients until just combined.

Incorporate buttermilk, eggs, and vanilla extract, stirring gently until smooth.

Divide the batter between prepared cake pans and bake for 30-35 minutes, or until a toothpick comes out clean.

Allow cakes to cool in pans for 10 minutes, then turn out onto a wire rack to cool completely.

Whip heavy cream in a medium bowl until stiff peaks form, then fold in semi-sweet chocolate chips.

Blend cream cheese, melted white chocolate, confectioners' sugar, unsalted butter, and lemon juice until smooth.

Layer one cake on a serving plate, spread half of the chocolate mousse over it, and top with a layer of cream cheese frosting. Repeat with the second layer.

In a saucepan, heat additional chocolate chips, heavy cream, and sunflower oil until melted, then cool slightly.

Pour the ganache over the assembled cake and decorate with additional frosting, truffles, and cookie wafers.

Serve and enjoy the decadent layers!