Preheat the oven to 170°C/325°F/gas mark 3. Grease a deep, 23cm/9inch round cake tin with a removable base and line the bottom with baking parchment.
Place the butter and sugar in a large bowl and beat with an electric mixer until pale and fluffy.
Place the cardamom pods in a mortar and bash with a pestle until the seeds come away from the pods. Discard the pods and grind the seeds to a fine powder.
Sift together the ground cardamom, nutmeg, almonds, flour, baking powder and salt.
Whisk the eggs into the butter mixture one at a time, whisking well after each addition. Add a heaped spoonful of the dry ingredient mixture with each one to help prevent the mixture from curdling.
Scrape the batter into the prepared tin and level the surface. Bake for about 45 minutes until a skewer inserted into the center comes out clean or with a few moist crumbs. Cover the top of the cake loosely with tin foil halfway through baking if it begins to darken too much.
When the cake has nearly finished baking make the syrup. Place the caster sugar, lemon juice and rosewater in a small pan over a low heat and stir until the sugar has dissolved.
Leave the cake to cool in the tin for 10 minutes then carefully turn it out onto a wire rack. Poke holes in the top of the cake with a toothpick then brush the syrup all over the top of the cake making sure that it soaks all of it up. Leave to cool completely.
To make the icing, sift the icing sugar into a bowl and gradually stir in the lemon juice until it reaches a thick but pour-able consistency. Spoon the icing all over the top of the cake and gently coax it towards the edges with the back of a spoon.