In a small saucepan, combine the whole milk, granulated sugar, brown sugar, cornstarch, and sea salt. Heat over medium heat until the mixture is warm but not boiling. Remove from heat and add the semisweet Belgian chocolate and vanilla extract. Stir until the chocolate is completely melted and the mixture is smooth. Set aside to cool.
In a large mixing bowl, whisk together the all-purpose flour, baking powder, baking soda, and sea salt. In a separate bowl, combine the Dutch-processed cocoa powder, granulated sugar, and packed brown sugar. Mix well and set aside.
Using an electric mixer, beat the unsalted butter until creamy and smooth. Gradually add the cocoa mixture to the creamed butter, mixing until fully incorporated.
In another bowl, whisk together the buttermilk, strong brewed coffee, and vanilla extract. Add the room temperature eggs and mix until well blended.
Gradually add the chocolate mixture into the butter mixture, mixing on low speed. Alternate adding the flour mixture and the buttermilk mixture until everything is well combined and smooth.
Preheat your oven to 350°F (175°C). Grease and flour the two 9-inch round cake pans. Divide the batter evenly between the pans and bake for 30-35 minutes or until a toothpick inserted in the center comes out clean. Once baked, allow the cakes to cool in the pans for 10 minutes before transferring them to a cooling rack.
In a saucepan, combine the Belgian semisweet chocolate and unsalted butter. Heat gently until melted and smooth. Stir in the hot water, light corn syrup, and vanilla extract. Mix until well combined and glossy.
Once the cakes have completely cooled, place one layer on a serving platter. Spread a generous layer of ganache over the top, followed by a sprinkle of cake crumbs and toasted peanuts or almonds. Place the second layer on top and cover the entire cake with the remaining ganache. Decorate with more cake crumbs and nuts if desired.
