Preheat oven to 200 °C / 400 °F. Line baking sheets with parchment paper.
Place the diced butter, a pinch of salt and 125 ml (1/2 cup) of water in a sauce pan and bring to a boil over medium heat until the butter melted, twirling the pan occasionally.
Meanwhile boiling the mixture, beat the eggs well in a bowl.
Remove from the heat and add the shifted flour and quickly stir with a wooden spatula/spoon until well blended.
Bring it back on the stove and continue to stir over low heat for 30 seconds.
Remove from the heat and add 1/3 of the beaten egg to the mixture in the pan and quickly stir.
Add the remaining beaten egg little by little, stirring each addition until it become like pastry cream but a little thicker. More specifically, if you lift up the spatula from the cream puff paste, the paste with the spatula holds a few seconds and fall down very slowly. Some of the beaten egg will be remained.
Place the puff pastry sheets on the parchment paper. Then evenly place the cream puff paste on the center of the each puff pastry sheets with a spoon, making about 6 cm (2 1/2 inch) circles.
Gently wrap the cream puff paste with the puff pastry sheets. Then brush the remained beaten egg on the pie sheets.
Bake for 20 minutes. Then reduce the temperature to 180 °C / 350 °F and continue to baking for another 20 - 25 minutes until crispy. Do not open the oven throughout the baking process.
When baking is finished, leave the cream puffs in the oven with the door closed for 10 minutes. Then remove from the oven and cool down to room temperature.