Cream together the butter and sugar until light and fluffy.
Bash the cardamom pods in a pestle and mortar, then remove the shells, and crush the insides to a powder. Zest the lime too.
Add the flour, salt, baking powder, lime zest and crushed cardamom to the butter and sugar. Mix together with a spatula until a dough forms. Roll into a ball and cover with cling film, then refrigerate or 30 minutes. While the dough chills, preheat the oven to 180°C.
Once chilled, roll the dough out quite thin on a floured surface, about 3 mm thick. Cut into whatever shapes you like, I used a round fluted cutter. Chill again for another 10 minutes or so (this will help the biscuits keep their shape, if they're just circles you can skip this step).
Bake for 8-10 minutes until the edges are turning golden brown. Then take out of the oven and leave to cool. They might feel soft when you take them out but they should harden up as they cool.
To make the glaze, crush the cardamoms to a fine powder, add the lime juice into a small bowl. Miz in the icing sugar and cardamom. You want a thick gloopy white mixture, so add more icing sugar if you need to. Drizzle onto the cooled biscuits with a teaspoon and sprinkle on the extra lime zest.