Preheat the oven to 220 degrees Celsius (420 degrees Fahrenheit).
Place water, butter, salt and sugar in a pot. Melt it all together and then bring it to a rapid boil. Once boiling, add the flour to the pot and cook it out for about 30 seconds or till you see a film on the bottom of the pan. Once it all comes together, transfer to a stand mixer and beat out the steam, then slowly add one egg at a time, beating well to incorporate in between.
Spoon your choux mixture into a piping bag with a star or round wide nozzle. Pipe two rows of well-spaced logs onto each cookie sheet. Bake one tray at a time for 25 minutes, reducing temp to 200 degrees Celsius (400 degrees Fahrenheit) as soon as they go in the oven.
Combine the sugar and potato starch in a pot. Whisk in the eggs, egg yolks, lemon zest, and lemon juice until blended.
Turn the heat to medium and cook the mixture, whisking continuously, until it is thick and bubbly, about three to four minutes. Whisk for one minute longer, then remove from the heat.
Place a strainer over a medium bowl. Pour the lemon mixture through the strainer, using your whisk to push it through. The zest and egg solids will get caught in the strainer and should be discarded.
Lay a sheet of plastic wrap directly on the lemon curd, touching the surface so that it does not form a skin. Put in the fridge to cool completely.
Place the sugar and water in a pan over high heat. Bring to a boil, then reduce heat to low and cook for four minutes.
Place egg whites in the bowl of an electric mixer and whisk on high until soft peaks form. While the motor is running, add the hot sugar syrup in a thin, steady stream and whisk for one to two minutes or until thick and glossy.
Let the eclair shells cool when they come out the oven for about 10 minutes.
When cooled, pipe the lemon curd into the shells.
Pipe the meringue on the eclairs, and then, using a kitchen blowtorch, torch until lightly golden.