Assemble ingredients for dough.
Cut butter into 1-2cm cubes and freeze.
Add flour, salt, sugar and cream of tartar to food processor bowl, pulse a couple times.
In a 250ml measuring jug beat egg, apple cider vinegar and enough iced water to make 135ml total fluid. Refrigerate until required.
Add frozen butter to flour mix and process until butter is between the size of a lentil and a small pea.
With the food processor running, stream in egg mix down the shute and process until just combined. When the food processor engine starts to rumble stop.
Turn out the dough onto a clean kitchen bench. The dough will be crumbly.
Gather the dough together using a bench scraper. Using the scraper, press the dough together and cut it in half. Then stack the halves on top of each other and press together. Repeat this a couple times until the dough starts to be less crumbly and form a dough.
Do not overwork the dough at this stage, it can look a bit rough and crumbly.
Divide dough in half and shape each half into a rough rectangle, wrap in plastic wrap or put in a sealed container and refrigerate for at least 30 minutes.