To make the cream mixture, heat the cream with the milk and sugar in a pot on the stove. Beat the egg yolks with the cocoa well and add the milk in a trickle, while stirring. Return the dish to the stove and stir continuously. Add the dissolved starch, essence and gelatin, which has swollen and melted in advance.
It is best to add the gelatin after removing the pot from the heat. Heat 1 cup of sugar until caramelized and add the chopped walnuts. Stir until you get a light caramel. Spread it on a flat surface and after it cools, crush it into tiny pieces. Put the layer in a baking dish or mold and gently syrup it with a little milk.
Smear it well with cream, sprinkle it with the caramel with walnuts, arrange the eclairs on top tightly and fill up with the rest of the cream.
Sprinkle again with the caramel with nuts and put the cake for 3 hours in the refrigerator. Having tightened well, arrange eclairs on top to decorate and top the entire cake with a glaze, made from the pre-melted couverture chocolate, liquid chocolate and 1-2 tablespoons butter.
Sprinkle again with the caramelized sugar and allow to set for 1-2 hours before serving.