Prepare sweet shortcrust pastry. Beat butter until soft and creamy. Add brown sugar, salt, egg and soy bean powder and mix well. Add both flours and fold in with a spatula. Wrap dough in cling wrap and rest in the refrigerator for 3 hours.
Unwrap dough and place on a non-stick baking mat. Cover dough with cling film and roll out to a thickness of 3–5 mm. Remove no