Whizz up the flour, icing sugar and COLD butter (cut up into squares), until it looks like breadcrumbs.
Then add the yolk.
Add COLD water until it forms a loose dough.
Knead together briefly.
Wrap in Cling Wrap and place in the fridge for a minimum of 20 minutes.
Take out and use as required.
Can be frozen.
Ensure fully thawed before use.