Put the water and Trex into a saucepan. Heat gently, so that the Trex melts, then bring up to the boil. Remove from the heat, then immediately add all the flour, beating vigorously with a wooden spoon so that the mixture forms a soft ball. Cook over a low heat for about 30 seconds. Cool for 5 minutes.
Gradually add the beaten eggs to the flour mixture using either a hand-held electric mixer or a wooden spoon, beating well between each addition. The mixture should be very smooth, shiny and thick.
Spoon the mixture into a large piping bag fitted with a plain nozzle. For eclairs, pipe twelve 10cm (4in) lengths on the baking sheets, allowing room for them to spread and rise. For profiteroles, pipe about 30 balls instead.