Preheat oven to 160°C/320°F or 140°C (fan forced / convection).
Grease and line a 31.5 x 23.5 cm / 9 x 13" baking tray with baking paper on the bottom and overhang from the sides. The overhang will help in easily taking out the shortbread cookies later.
Place the softened butter in a medium sized bowl. Beat butter until pale and creamy. Sift over the icing sugar (powdered sugar) and combine together.
Add the cardamom powder and lemon zest and stir together.
Add the flour in two portions. First mix one cup of flour, and then add the other. Beat until the dough comes together. Use your hands to turn the dough into a smooth ball of dough. Don't knead.
Roughly shape the dough into a rectangle shape, and place it into the prepared tray. Use a rolling pan, along with your fingers to press the dough into the pan. Be very light in rolling as well as pressing the dough, as that can make the biscuits firm.
Use a large sharp knife to score the shortbread into the shape of bars – don’t cut all the way through. Prick with a fork (2 to 3 times per bar).
Bake for 25 – 30 minutes, turning the tray halfway through the baking process, until the shortbread is light golden. Place the baking tray on a cooling rack to cool completely. This recipe makes about 22 - 24 cookies. Nutrition yield is for a serving of 1 cookie per person.
For the lemon glaze:
Place the icing sugar (powdered sugar) in a bowl and add the lemon juice. Mix together till a liquid glaze is formed. In case the glaze is too liquid, add more icing sugar (powdered sugar) and if it is too thick add a drop of lemon juice (or water). Drizzle the lemon glaze over the cooled shortbread biscuits.