First things first, pop the butter in a saucepan with 150ml of water. Heat gently on a low heat until the butter has melted, then turn up the heat and bring to the boil. Once boiling remove from the heat and immediately mix in the flour, beating well with a balloon whisk until thick, glossy and smooth – the mixture should form a soft ball of dough in your saucepan. Pour your ball of dough into a heatproof bowl and leave to cool for 10 minutes.
Gradually pour in the beaten eggs and whisk well between each addition until you have a thick, glossy mixture, you may not need to add all your egg so keep an eye on the consistency of your mixture.
Your choux pastry is now ready to pop into a piping bag and pipe into choux buns or eclairs!