Put butter, water, salt and sugar in a saucepan and let it boil. Take the pot off the hob. Add the flour and continue cooking until the dough forms a ball.
Take the pot off the hob and gradually add an egg and stir well. Pour the batter into a piping bag. Use a piping bag to sprinkle the éclairs on a baking tray and bake in the preheated oven at 200 degrees for 20-25 minutes.
Fill the éclairs with the pudding. Dip the éclairs in the melted chocolate and let them dry.
Tip: Melt 2/3 of the chocolate over a water bath and remove from the water bath. Then add the rest of the chocolate and melt. This is how the chocolate is tempered.