Place the egg yolks and sugar in the bowl of a stand mixer and beat until light and fluffy. Add the cocoa powder, vanilla, and brandy. Beat until well combined. Add the chopped walnuts and fold them in with a spatula.

Place the egg whites in a clean, dry bowl and beat until they form stiff peaks. Add one-third of the meringue to the yolk mixture and gently fold using upward, circular motions to lighten the mixture. Add the remaining meringue and fold gently until incorporated.

Pour the mixture into a rectangular baking dish measuring about 22 × 32 cm (approximately 9 × 13 inches). Bake at 160°C (320°F) fan, for 20 minutes.

Remove the dish from the oven and stir the mixture thoroughly with a spoon. It may look uncooked in the center and cooked around the edges, but that is exactly how it should be.

Transfer the mixture to the serving dish or bowl in which you will serve the dessert and spread it evenly over the bottom.

Place the milk, heavy cream, and sugar in a saucepan over medium-high heat.

In a bowl, whisk together the eggs, egg yolks, and cornstarch until the cornstarch has dissolved. Add the vanilla and mix well.

As soon as the milk-and-cream mixture comes to a boil, add the chocolate and stir until completely melted.

Remove the saucepan from the heat. Slowly pour the hot milk mixture into the bowl with the eggs, whisking constantly with a whisk or using a mixer.

Transfer the mixture to a clean saucepan and cook over medium-low heat. Stir constantly until the cream boils and thickens. Keep stirring for a minute.

Add the butter and stir until melted and fully incorporated.

Pour the chocolate cream over the walnut base. Spread it evenly, then press plastic wrap directly onto the entire surface of the cream. This will prevent a skin from forming.

Allow the dessert to cool to room temperature. Then refrigerate until completely chilled.

Whip the heavy cream with the powdered sugar until light and fluffy and it forms soft whipped cream.

Remove the plastic wrap from the chocolate cream and spread the whipped cream evenly over the top.

Dust with cocoa powder before serving.