In a saucepan, combine the water, milk, butter in pieces, salt, and sugar.

Place the saucepan over medium heat and bring the mixture to a boil.

Quickly add all the flour at once, stirring continuously to form a dough. Reduce the heat to medium and continue cooking for a few more minutes.

The dough should come together in a ball, with a smooth crust forming at the bottom of the saucepan.

Remove from heat and allow to cool until warm.

In a separate bowl, it's easier to mash the eggs using an immersion blender, but a fork works as well.

Gradually add the egg mixture to the cooled dough, using a stand mixer with a paddle attachment or a hand mixer with dough hooks to mix.

Mix each portion of eggs thoroughly before adding more. It's important to observe the consistency of the dough; you may need slightly more or fewer eggs.

The final dough should be shiny and fall from the whisk in wide, thick ribbons.

Using a piping bag or a spoon, place dollops of dough approximately 3-3.5 centimeters apart on a baking mat.

Be sure to give them space as they will puff up nicely during baking.

Bake in a preheated oven at 170 degrees Celsius (about 340 degrees Fahrenheit) for 40-45 minutes until golden brown.

Do not open the oven door during baking to ensure they rise correctly.

Heat the milk in a saucepan until it reaches a boil.

In a bowl, whisk together the egg yolks, sugar, flour, and cornstarch until well combined.

Slowly pour a third of the hot milk into the egg mixture while whisking continuously to temper the eggs.

Then pour in the remaining milk while continuing to stir to avoid lumps.

Return the mixture to the saucepan and cook over medium heat, stirring constantly. Once it comes to a boil, cook for an additional couple of minutes until thickened.

If using gelatin for stability, stir it into the hot mixture. Allow to cool to about 40 degrees Celsius (approximately 104 degrees Fahrenheit).

Finally, mix in the room temperature butter until fully incorporated and chill in the refrigerator for a couple of hours until stabilized.

Using a piping bag fitted with a small nozzle, fill each cream puff with the chilled vanilla pastry cream.

You can also make a small cut in each puff and spoon in the cream if preferred.

Before serving, dust with powdered sugar for an elegant touch.