Weigh the flours, xanthan gum, baking powder and salt into a large bowl and mix together until evenly combined.
Add the butter and lard/Trex to the bowl and rub the into the flour mixture using finger tips, until it resembles coarse breadcrumbs.
In a small bowl, beat the egg with the water and then pour into the crumb mixture.
Stir the wet ingredients into the crumb mixture using a table knife until it begins to clump together.
Once it is beginning to come together as a dough, leave the mixture to stand for 5 to 10 minutes to fully absorb the liquid.
Finally, bring the dough together with your hands and press into a ball.
If not using immediately, wrap and refrigerate. And when ready to use, take from the fridge and knead very lightly to enable it to become 'rollable'.
* Note: nutritional information is an estimate & may vary according to portion size/ingredient variants.Gluten Free Alchemist Flour Blend B can be found on the GFA Flours & Flour BlendingPage. If using an alternative flour (particularly one which is heavily rice-based), the texture may be slightly different and more liquid may be required.