Beat the eggs with 1 4/5 cups (450 g) powdered sugar until white. Start adding the pre-sifted flour with baking powder and vanilla. Finally, add and mix with the cocoa and zest. If the mixture seems too thick, add 1/2 cup oil. Pour the mixture into a greased and floured tray and put it to bake in a moderate preheated 392°F (200 °C) oven.
The finished layer is cooled slightly and divided into 2 separate layers. To prepare the cream, dissolve the starch in the milk and put the cream in a water bath to thicken, while stirring. Sweeten with 2 tablespoons crystal sugar.
Separately, beat the butter with 2 tablespoons powdered sugar and add a packet of vanilla and the remaining cocoa. Melt the chocolate gently in a water bath and gently mix it with the cocoa mixture. Once the milk cream is slightly cool, mix it while stirring with the chocolate one.
Finally, add the ground walnuts. Put one layer in a tray, spray it lightly with milk and put a little less than half of the cream. Put the other layer on top, sprinkle it with a little milk and smear the entire cake well with the remaining cream.
Make a decoration of your choice. Leave the cake with cream in the refrigerator for several hours.