Preheat your oven to 350°F (175°C). Line three 8-inch round cake pans with parchment paper and generously butter the pans to prevent sticking.

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

In a separate bowl, whisk the eggs, vegetable oil, buttermilk, and sour cream until the mixture is smooth and cohesive.

In a small bowl, combine the cocoa powder and instant coffee. Pour the boiling water over the mixture and whisk until it forms a smooth, shiny liquid.

Gradually add the dry ingredients to the wet ingredients in two additions, folding gently with a spatula until just combined. Then, incorporate the cocoa mixture, folding carefully to avoid overmixing.

Evenly divide the batter among the prepared cake pans. Bake for 22–24 minutes, or until a toothpick inserted in the center comes out with moist crumbs. Allow the cakes to cool in their pans for 20 minutes before transferring them to a wire rack. Chill the cooled layers in the refrigerator for at least 1 hour.

In a saucepan, melt the dark chocolate with the corn syrup over low heat, stirring constantly. Set aside to cool slightly. In the bowl of a stand mixer fitted with the paddle attachment, beat the cream cheese, cocoa powder, powdered sugar, and salt on medium speed until creamy and smooth. Add the heavy cream and mix on low speed until fluffy. Slowly pour in the melted chocolate and mix until fully combined. Allow the frosting to cool to a spreadable consistency at room temperature for approximately 30 minutes.

Use a serrated knife to trim the domed tops of the cake layers, ensuring they are flat. Place one cake layer on a serving plate and spread a generous amount of frosting over the top. Repeat with the second and third layers, then cover the entire cake with a thin crumb coat of frosting. Refrigerate for 20 minutes to set the crumb coat. Finish by spreading the remaining frosting over the cake, smoothing with an offset spatula.