Make the chocolate pudding: In a saucepan over medium heat whisk together 1/4 cup granulated sugar, 1/4 cup packed brown sugar, 2 tablespoons cornstarch, 1/4 teaspoon sea salt, and 1 1/2 cups whole milk. Cook, stirring constantly, until the mixture thickens and comes to a gentle boil; reduce the heat and cook 2 more minutes, stirring.

Remove the saucepan from the heat and stir in 6 ounces semisweet Belgian chocolate (chopped) until melted and the pudding is smooth. Stir in 1 teaspoon vanilla extract. Transfer the pudding to a bowl, press plastic wrap directly onto the surface, and refrigerate at least 2 hours or until cold and set.

Preheat the oven to 325°F. Grease four 8-inch round baking pans and line the bottoms with parchment paper.

In a medium bowl whisk together 1 1/2 cups all-purpose flour, 2 teaspoons baking powder, 1/2 teaspoon baking soda, and 1/4 teaspoon sea salt. Set aside.

In a large saucepan over medium heat melt 1/2 cup unsalted butter (cubed). Add 1 cup Dutch-processed cocoa powder and stir to form a smooth paste; cook 1–2 minutes, stirring, taking care not to burn the cocoa.

Stir in 1 cup granulated sugar and 1 cup packed brown sugar until dissolved. Add the 6 ounces Belgian dark chocolate (melted) and stir until completely incorporated and smooth.

Remove the pan from the heat and stir in 1 cup buttermilk, 1 cup strong brewed coffee, and 1 teaspoon vanilla extract until combined.

Whisk in 2 large eggs, one at a time, until fully incorporated.

Gradually add the flour mixture to the chocolate mixture, stirring until the batter is smooth and homogenous.

Divide the batter evenly among the prepared pans and bake about 35 minutes, or until a toothpick inserted in the center comes out clean or with just a few moist crumbs.

Cool the cakes in their pans for 10 minutes, then invert onto cooling racks and cool completely.

Make the chocolate frosting: Melt 16 ounces Belgian semisweet chocolate (chopped) and 1 cup unsalted butter (cubed) together in a double boiler or in the microwave in 30–40 second increments, stirring until smooth. Gradually whisk in 2/3 cup hot water, 2 tablespoons light corn syrup, and 1 teaspoon vanilla extract until glossy and combined. Chill in the refrigerator 25–30 minutes, or until the frosting is thickened and spreadable.

Prepare cake crumbs: Using a long serrated knife, trim the top (domed portion) off each cooled cake layer to make each layer flat. Put the trimmed cake pieces in a bowl and crumble them by hand to make cake crumbs; reserve the crumbs for decorating.

Assemble the cake: Place one cake layer on a serving plate. Spread an even layer of the chilled pudding over the layer. Repeat with the remaining layers, stacking them as you go and spreading pudding between each layer.

Frost the stacked cake: Use the chilled, spreadable chocolate frosting to cover the top and sides of the stacked cake. If desired, reserve a small amount of frosting to pipe roses on top.

Decorate the sides and top: Press the reserved cake crumbs onto the sides of the cake. Sprinkle and press 1/2 cup toasted peanuts or almonds onto the sides and/or top as desired.

Refrigerate the finished cake for at least 8 hours (or overnight) before serving to allow the layers and frosting to set.