Preheat over to 350F. Prepare a baking tray with parchment paper. Trace out eight 5cm circles onto the parchment paper and flip over. Ensure there is 1in of space around each circle.
Bring water, milk, butter, salt and sugar to boil over a medium heat.
Remove from heat and add flour all at once. Once there are no more lumps, put back on medium heat.
Cook dough while stirring constantly for 2 more minutes. It should form a ball and there may be a film of dough at the bottom of the pan.
Transfer to another bowl and mix to cool down for around 2 minutes.
Whisk eggs together in a small bowl. Add ⅓ of egg mixture to the dough at a time until it is the right consistency. You are looking for a smooth and glossy dough that holds its shape. It will have a V shape when you pull your spatula up.
Transfer dough to a piping bag with a lare round tip. Pipe out onto the prepared parchment paper.
Take out craquelin and cut out 6 cm circles using a cookie cutter. Place each circle on top of the choux dough.
Bake for 30 minutes until choux pastries are crispy.
Let cool completely before filling with the matcha pastry cream. These are best enjoyed fresh. If you are not eating it right away, don't fill the choux buns until you plan on eating them, they may become less crispy!