Zest one of the oranges and squeeze out the juice of both the oranges. This should measure around ⅓ cup. Place the eggs and sugar in the bowl of an electric mixer and whisk until thick, pale and doubled in volume, around 5 minutes.
Combine the juice and butter and add to the egg mixture in two batches, folding through until combined. Sift in the flour and cardamom and add the ground pistachios and fold through the mixture.
Cover and leave to rest in the refrigerator for at least 1 hour, or overnight.
When you are ready to bake the madeleines, preheat the oven to 180 Celsius 350 Fahrenheit. Butter and flour a 12-shell madeleine tin and place heaped tablespoons of the batter into each mould.
Bake for 8 to 10 minutes or until golden and cooked through. Transfer the madeleines to a wire rack to cool and wash, dry, butter and flour the tin and repeat with remaining batter. Dust with icing sugar and cardamom and serve warm.