In a saucepan, bring milk, water, butter, sugar and salt to a boil, then remove from heat, add in sifted flour and cocoa powder while stirring continuously until a smooth dough is obtained.
Continue to cook the dough over medium heat until a thin layer of skin is formed at the bottom of the saucepan.
Place the dough in a mixing bowl with paddle attachment, mix and cool down the dough to 45˚C, gradually add in whole egg, and followed by milk, adjust the dough with milk by getting 820g, total weight of the dough.
Mix again the dough at medium speed until a smooth choux paste is obtained.
