Put the flour and salt into the bowl of a food processor

Cut the cold butter into small dice sized pieces and add to the bowl

Use the pulse button and in short bursts blitz the flour so that it lifts and mixes, and forms a breadcrumb consistency.  A few short pulses will do the trick.

You do not want a sticky ball as your pastry will be hard and dense if this happens.

Add the sugar and blitz again quickly.

Add the eggs and yolk and pulse until the pastry just comes together.

Remove from the bowl , turn it out onto a floured board and knead by holding the pastry in both hands and pressing down with your thumbs, then turn the pastry and repeat a few times until it comes together.

If the dough is too sticky add a little flour to the board and knead again.

Fold the pastry over itself and press down with your fingertips.  Repeat.

Rest the pastry by wrapping it in greaseproof paper (not cling film which will make it sweat) and leave in the fridge for at least an hour, preferably longer or overnight. (or in the freezer for 15 minutes if you are in a huge hurry)

By resting the pastry it allows the gluten to relax so that the pastry becomes more elastic and is easier to roll.  By resting it also prevents your pastry from shrinking from the sides when it cooks.