1weigh out your flour and fat precisely. and put some cold water in a jug
2Food processor - normal blade - flour in first (so that the fat doesn't just clog under the blades - yep I've done that). fat cubed on top
3Blitz for about 30 seconds for it to turn to breadcrumbs
4turn on again. add a weeny bit of water at a time through the funnel thingy
5you've added enough water when the (now dough) comes clean off the sides (pictured)
6turn out onto a lightly floured surface and form into a ball.
7wrap tightly in clingfilm and refrigerate for AT LEAST 30 Minutes - This is when the water activates the gluten in the flour. It makes it all stay stuck together. Don't skip this step otherwise when you go to roll it out it will return to crumbs!
9Tip - you've followed all the steps but when you go to roll it out it breaks when you pick it up - not enough water - there hasn't been enough to activate the gluten in your flour. DON'T BIN IT JUST YET. Return it to the food processor and blitz back to breadcrumbs. then add more cold water (a little at a time) until its back to a dough until the sides of your food processor jug is clean?. It will feel damp but not wet - i wish i could explain that better. Anyway, again form into a ball, wrap and refrigerate for 30mins then try rolling again