Start by preheating your oven to 350°F (175°C). Grease and flour your two 9-inch round baking pans.
In a medium saucepan, combine the whole milk, chopped semisweet Belgian chocolate, and 1 teaspoon of vanilla extract. Heat over medium-low, stirring until the chocolate is melted and the mixture is smooth. Set aside to cool slightly.
In a large mixing bowl, whisk together the all-purpose flour, baking powder, baking soda, cocoa powder, granulated sugar, brown sugar, and sea salt. Make sure everything is well combined.
In another bowl, beat the cubed unsalted butter until creamy and smooth. Gradually add the dry mixture to the butter, alternating with the buttermilk and the chocolate milk mixture. Mix until just combined.
Add the room temperature eggs and brewed coffee to the batter, mixing until everything is smooth and well incorporated. Be careful not to overmix.
Evenly distribute the batter into the prepared baking pans. Bake in the preheated oven for 30-35 minutes or until a toothpick inserted into the center comes out clean. Once baked, remove the cakes from the oven and let them cool in the pans for about 10 minutes before transferring them to a cooling rack.
While the cakes are cooling, prepare the frosting. Melt the Belgian semisweet chocolate and let it cool slightly. In a mixing bowl, beat the cubed unsalted butter until creamy. Gradually add the melted chocolate, light corn syrup, and 1 teaspoon of vanilla extract, mixing until fluffy. If necessary, add a little hot water to reach your desired consistency.
Once the cakes are completely cool, place one layer on a serving plate. Spread a generous amount of chocolate frosting on top. Place the second layer on top and frost the top and sides of the cake. For a decorative touch, use cake crumbs and sprinkle toasted peanuts or almonds on top.
For the best flavor and texture, chill the cake in the refrigerator for at least an hour before serving. This allows the frosting to set and makes slicing easier.
