In a sauce pan on medium heat, add water, milk, butter, salt and sugar. Stir to make sure the butter melts. Reduce the heat before it reaches a boil.
When it reaches a simmer, add the flour. Mix the flour and make sure all the lumps are gone. The mixture will form a rough ball. Using a wooden or rubber spatula, continue to press and stir for about a minute to allow the mixture to cook.
Remove from heat and transfer to your stand mixer with the paddle tool or a bowl if you use a hand mixer. Let the mixture cool down a bit: don't add the eggs to a hot mixture as they may scramble.
Lightly beat the eggs.
Turn on your mixer. Add a quarter of the eggs to the mixture. The mixture will break up and look curdled - don't be alarmed, it will come together quickly. Add the following quarter, incorporate and add the third. The fourth quarter of the egg you add carefully: if the mixture looks nice and yellow, shiny, thick but you can still easily pipe, you can stop.
Add the mixture to a piping bag with a large round nozzle and set aside. You can use a spoon to scoop the mixture, but it's harder to make them similar in size, shape and looks.