Make the shortbread dough. Cream the butter and sugar and add the egg. Sift the flour and cocoa powder together, and fold into the butter mixture. Let the dough rest in the refrigerator for 1 hour.

Make the choux pastry shell. Sift the flour and cocoa powder together. Beat the eggs. In a sauce pan over medium heat, add the butter, hot water, and sugar. Bring it to a rapid boil.

Turn off the heat and add the dry ingredients. Mix the liquid and dry ingredients until well incorporated. Once it becomes a lump, turn on the heat again and knead it briefly.

Turn off the heat and gradually add the beaten eggs. It seems to separate at first, but gradually becomes easier to add the eggs. Mix well each time adding the eggs.

The right consistency to stop adding the egg is when if you scoop it up with a spatula, the dough drops leaving a triangle stream on the spatula.

Add the choux pastry dough into a piping bag and pipe it out into 3-4 cm circles.

You will use about 5 g of shortbread dough per choux pastry shell. Roll out the dough in your palm into a ball, hold it in between plastic wrap and spread it into 5 cm circles. Cover the choux pastry dough with the shortbread dough.

Start baking the dough at 200℃. After 20 minutes, reduce heat to 160℃ and bake another 10 minutes.

Bake it a total of 30 minutes. Do not open the oven door while baking!! After the dough is done cooking, leave the door closed and leave it as it is until the shells are cool and dry.

Make the cream. In a microwave-safe container, add the egg and sugar and mix well. Add the flour and mix until smooth. Add the vanilla and milk.

Microwave it for 4-5 minutes without plastic wrap. Take it out a few times and stir well each time. Place it on top of ice water to cool it down.

Beat the heavy cream until firm peaks form and add the chilled custard cream. Mix well and the crème diplomat is done.

Cool off the choux pastry shells, make a slit in the middle and add a lot of cream.