Heat the water and the milk with the butter. When the mixture is cooking, add the flour. Mix to a dry dough ball.
Remove from the heat and continue working in a mixer. Let the dough ball rotate, with the spatula, until almost no more vapor is coming out from the bowl.
Incorporate the eggs (at room temperature) into the dough. Add them little by little and give the dough the time to absorb them. When 22 eggs are incorporated, check the firmness of the dough (look if the dough forms a stiff peak). If the dough is too firm, add the remaining egg.
Remove the bowl from the mixer and mix briefly with the spatula by hand to obtain a homogeneous dough. Cover with a damp cloth and let the dough rest (30 minutes-1 hour).
After the rest, put the dough into a piping bag. Use a star nozzle (16 mm) with many teeth. Pipe the choux pastry on a buttered baking tray.
Spray with a baking spray just before baking.
Bake at 175 °C in a floor oven for 30 minutes, then raise the temperature to 210 °C and bake for another 10 minutes.