Preheat the oven to 180°C and grease two 20cm tins with baking paper.
Beat butter, eggs, sugar, flour, and baking powder in a bowl until combined.
Crush cardamom seeds finely and stir them into the cake batter.
Divide the batter into tins and bake for 25 minutes until golden.
Melt white chocolate over a pan of simmering water and let it cool slightly.
Whisk butter, cream cheese, icing sugar, and vanilla together before stirring in chocolate.
Slice cakes horizontally and layer with icing to create four sponge layers.
Dust the top with icing sugar using a decorative stencil.