Steps

• Butter and flour the mold, turn on the oven to 350°F.
  Place the whole eggs in the bowl (the eggs must be at room temperature), add the sugar and a pinch of salt (vanilla aroma or vanillin if desired).
  Turn on the beaters and whip the mixture.
  The mixture should be fluffy and light.
  (To achieve this result, the beaters must beat for 6/8 min.)

  

• Gently add the flour and the potato starch, previously sifted.
  Mix with the whisk from bottom to top.
  Be careful not to deflate the mixture.

  

• Pour the obtained mixture into the buttered and floured mold. (Mold 10.6×7.9 inches).
  Bake for 15/17 min. at 350°F (the oven must be already hot).

  

• Let it cool before removing it from the mold.

  

• Now take your ready-made puff pastry and roll it out slightly with the help of a rolling pin.
  Transfer it to a baking tray with its baking paper, and prick it with a fork or the appropriate wheel.
  Sprinkle with powdered sugar. Do the same for the other one and bake in a preheated static oven at 350°F for about 15 minutes (until they are well golden).
  If you bake them together, you can swap the trays halfway through cooking.
  For a perfect bake, of course, adjust according to your oven.

• My advice is to prepare the cream well in advance; we need it nice and cold.
  Pour the milk into a saucepan, then bring it to a boil with the whole lemon peel, being careful to only get the yellow part.
  (I used lemon peel but a vanilla bean or a tablespoon of vanilla extract is also fine).
  In a separate saucepan, work the eggs with the sugar. (Whole eggs, both yolk and white).
  
  Then add the flour, stir with the whisk to remove any lumps.
  (If you want, you can replace the flour with cornstarch).
  Thin the mixture with a little milk poured in a trickle, being careful, to avoid the lemon peel ending up in the cream, use a strainer, after adding all the milk put it back on moderate heat.
  
  Put it back on the heat and always stirring you will see that the custard will thicken in a few seconds.
  Turn off the heat and cover the quick custard with plastic wrap placed in contact.
  As soon as the custard has cooled, pour the fresh cream into a bowl, add the powdered sugar and work it with electric whisks until it is semi-whipped.

  

• Soften the custard by working it with a whisk.

  Now add the cream to the custard little by little, stirring gently with a spatula.

  

• In a saucepan place the water with the sugar and bring to a boil. Let the syrup cool and add the Alchermes.

• When the sponge cake is cold, trim it both at the top and bottom to remove the crust.
  Trim it laterally to obtain a rectangle measuring 9.4×6.3 inches.
  
  When the puff pastry is cold, trim it laterally to obtain a rectangle of the same size.
  Repeat this operation also for the second layer.
  Now we need to assemble the diplomatic cake. Take a rectangle of puff pastry that will serve as the base and spread half of the diplomatic cream on it with the help of a spatula.
  Place the sponge cake on top.

  

• Brush it well with Alchermes.
  Place the remaining cream, spread it with a spatula, and finally position the last puff pastry rectangle on the cream.
  
  Transfer to a dish, cover with plastic wrap, and place in the fridge for an hour.

  

• After the time has elapsed, dust with powdered sugar and it’s ready to be served.

  

• Enjoy your meal