Mix shortbread ingredients into a soft dough and knead lightly until smooth.
Flatten walnut-sized pieces of dough onto baking sheets.
Bake at 170°C for 12 to 15 minutes until golden.
Cool slightly and break the shortbread into rough pieces.
Melt 15g of butter in a large frying pan.
Add rhubarb, sugar, cardamom, orange rind, and juice to the pan.
Cover the pan and poach until the fruit softens.
Remove the fruit and reduce the remaining juices if necessary.
Stir orange flower water into the pan off the heat.
Transfer the fruit mixture into individual ramekins or a die dish.
Top with crushed biscuits, dust with icing sugar, and serve with hot custard.