Put 150ml water, the butter and a pinch of salt into a medium pan and gently heat until the butter melts. Turn up the heat and bring to the boil.
As soon as it’s boiling, tip in the flour in one go. Beat quickly to combine. TIP: It’s important to tip the flour in as soon as the water boils, because losing too much liquid by evaporation will affect your pastry.
The starch in the flour needs to be cooked out now. Beat well, over the heat, until the mix turns smooth and glossy and starts to come away from the edge of the pan. Tip the mix into a bowl and allow to cool a little.
Give the mixture a quick beat, then start adding the eggs a little at a time, using a whisk, wooden spoon or electric beaters. You may not need to add all the egg – stop once the pastry is smooth and elastic and drops easily off a spoon. This step is probably the most difficult for beginners - knowing when to stop adding the egg. So I always recommend looking at the video and using the texture and consistency as a reference.
Heat oven to 220C/fan 200C/gas 7. Drop a medium nozzle into a large piping bag and scoop the pastry into it. Line two baking sheets with non-stick paper and pipe 15 x 10p-size balls of pastry onto each one.
Use a wetted finger to smooth the tops. TIP: The just-piped pastry buns have pointy tops, which can quickly burn. Tap them down gently with a wet finger before you put them in to bake.
Bake for 15-20 mins until dark golden and very firm. Transfer to a rack, turn each one upside down, then leave to cool. Will keep in an airtight container for up to 2 days.