For the choux doughnuts, boil the water with salt and butter, add the flour, stirring constantly. Stir the mixture until it separates from the edge and a white coating forms on the bottom.
Let cool a bit and then gradually incorporate the yolks. Pour the mixture into a piping bag and pipe doughnuts onto a baking tray lined with baking paper (leave space between them because they will rise).
Bake at 180 °C in a preheated oven until light brown.