For those of us in the UK I tweaked the amounts to suit our pack sizes etc better. You also need more water due to fiberflour being more absorbent than regular flour. Another great thing is that fiberflour comes out a little softer than regular plain flour so you won't have issues with tough pastry.
220g UF fiberflour
3/4 tsp salt
250g block unsalted butter, cold
170ml (approx) ice cold water
1. Mix UF fiberflour and salt together in a large bowl.
2. Cut butter block in half lengthways down the middle, then cut each piece again so you end up with 4 long squarish pieces (a bit like cutting the sponge for a battenberg cake).
3. Slice the butter into 1/2cm (quarter inch) thick slices and add to flour, tossing to coat.
4. Stir in enough cold water till a thick dough forms - you may need more or less water. There should be big lumps of butter visible (see picture 1 below).
5. Gather the dough into a ball, flatten into a disk shape then wrap in cling film or a freezer bag. Chill for 20-30 mins in the freezer or an hour in the fridge.
6. Unwrap dough and roll out on a floured work surface into a rough rectangle shape. Doesn’t matter how big the rectangle is as long as you can fold it as per the next step.
7. Fold the dough into thirds like folding a letter (i.e fold the bottom 3rd of the pastry towards the centre - see picture2 - then fold the top 3rd over that to end up with an envelope shape).
8. Turn dough 90 degrees, roll and fold again.
9. Repeat 2-4 times (or the more the better as long as the pastry doesn't get warm/ too soft). No need to chill the dough between rollings/foldings. You should still see blobs of butter in the pastry after you've finished the rolling/folding step (see picture 3).
10. Rewrap dough in cling film/freezer bag and chill for 2 hours or overnight.
Use pastry as required by your recipe either straight from the fridge or defrosted till thawed enough to roll.
This pastry needs to be baked in a preheated oven at 200 degC for around 10-15 minutes, then turn the oven down to around 180 degC to finish cooking so it doesn't burn. Do not bake at a lower initial temperature otherwise the butter will melt out slowly and you’ll be left with a soggy, greasy mess!
Uncooked pastry keeps for several days in the fridge or several weeks in the freezer.