Steps

• Pour the milk into a saucepan, then bring it to a boil with the whole lemon peel, taking care to use only the yellow part.
  (I used lemon zest but a vanilla bean or a tablespoon of vanilla extract works just as well).
  
  In a separate pot, work the eggs with the sugar. (whole eggs: both yolk and white).
  Then add the flour and whisk to remove any lumps.
  (If you wish, you can replace the flour with cornstarch).
  
  Temper the mixture with a little milk poured in a thin stream, using a sieve to avoid letting the lemon peel fall into the cream. After adding all the milk, return it to medium heat.
  Place it back on the heat and, stirring constantly, you will see the pastry cream thicken within a few seconds.
  
  Turn off the heat and cover the pastry cream directly with plastic wrap to prevent a skin from forming.
  Before using it, let it cool very well.
  (Tip: make it well in advance so that once cold you can keep it in the fridge).

  Once well chilled from the fridge, gently fold in the firmly whipped cream.

  

• 
  The first rule: the eggs must be at room temperature.
  So separate the yolks from the whites.
  Beat the egg whites to stiff peaks, adding the sugar while whipping.

  

• When the egg whites are well whipped, you can add the yolks one at a time so the mixture has time to incorporate them perfectly. (You can use a spatula or the beaters but reduce the speed).

  
  Add the last yolk and continue working with the beaters — the mixture must result well aerated.

  

• Yolks on top of the whipped egg whites.
  It’s time to start adding the dry ingredients: the all-purpose flour and the potato starch.
  Both should be sifted to avoid lumps that would ruin the cake.
  Continue working with the beaters to incorporate them perfectly.
  Now add the neutral oil in a thin stream so it incorporates evenly.
  Work again with the electric beaters, lowering the speed.

  

• Then bake in a preheated conventional oven at 392°F for about 10 minutes or until golden.
  The surface should become just golden and you must never open the oven, which will retain moisture inside.
  Remove the sponge cake from the oven, take it immediately off the tray and place it with the parchment paper on a kitchen towel, upside down.
  Begin to detach the sponge cake from the parchment paper carefully so as not to tear it.
  Place it on a clean sheet of parchment paper with the golden side visible on top.

• 
  
  The First Roll: While the sponge is still hot, start rolling the cake from the short side, including the towel between the spirals.

  This prevents the sponge from sticking to itself as it cools.

  
  Leave it like this, wrapped in the towel, until it is completely cool.

  This way the sponge “learns” the shape and, when you unroll it to add your diplomatic cream, it will unroll smoothly without cracking.

• Once cool, unroll the sponge.

  Before filling, trim part of the edge (the borders or a strip) and cut it into small, regular cubes on a cutting board, just as you see in my photo.

  

• Brush the remaining base with a strawberry syrup or fruit juice.

  Spread the diplomatic cream and place the strawberries in a single row down the center.

  Roll tightly.

  Keep a little diplomatic cream for the outside — just a thin coating.

  

• Cover the outside with a thin layer of cream and press the previously prepared cubes onto it.

  Finish with a dusting of powdered sugar, rosettes of whipped cream and fresh strawberries.

  

• Enjoy.