Bring the eggs to room temperature. Whisk them lightly to combine the whites and the yolks.
Preheat the oven at 240°C.
Sieve the flour.
Cut the butter into small cubes (maximum 2cmx2cm).
Place the milk, the butter, the salt and the sugar in the saucepan.
Bring to boil and as soon as it starts to boil remove from the heat (but don't switch off the stove).
Add ALL the flour in ONE GO. Mix immediately (off the heat) using the wooden turner (or a spatula not too flexible). Ensure there are no lumps at this stage.
Place the saucepan on the stove again (at medium heat) and mix energetically to dry the dough and evaporate the excess moist. This step should take 1 to 2 minutes (depending on the flour)*.
The dough is ready when it forms a thin film at the bottom of your stainless steel saucepan OR small oil droplets at the bottom of your non-stick saucepan*.
Transfer it into the bowl of the stand mixer equipped with the flat beater. Mix at low speed for 1 minute to cool it down and avoid cooking the eggs while adding them.
Add the eggs a little at a time (4 to 5 times) and mix (at low speed) after each addition*.
The dough is ready when it becomes smooth, glossy, lumps free, and holds its shape*.
Transfer the dough in the piping bag with the French star tip.
Make sure there are no air bubbles trapped in the bag before starting piping (by pushing the dough towards the tip)*.
Pipe 10 to 12cm long eclairs on the Silpat mat* (not recommended to use parchment paper here), at an 45° angle with a constant pressure. Make sure to leave 5cm gap in between.
Optional: place thin craquelin rectangles on top of each eclair.
SWITCH OFF the oven and bake for 10 minutes.
Switch on the oven at 170°C on STATIC mode (without opening the door) and continue baking for 15 minutes.
Open slightly the door of the oven (you can place a thin spoon to block it) and continue baking for 15 minutes. You may need more time depending on the size of your eclairs, your oven and how much you opened its door.
The eclairs are done when they have a nice dark golden color.
Let them cool on a cooling rack.