Combine together the flour and butter using a fork or food processor. You'll get a breadcrumb type consistency.
Start to slowly add water to the breadcrumb mixture to start to form the pastry together. I find that I typically use 60-75ml. Then the mixture is fairly wet but it dries up a little once chilling in the fridge.
Wrap in clingfilm and leave in the fridge for 1-2 hours before using.