In a large bowl, combine the flour, baking powder, cardamom and a pinch of salt. In another bowl, mix the buttermilk, egg yolks, orange zest and juice and butter. Pour the wet ingredients into the dry and whisk to create a smooth batter.
Whisk the egg whites until stiff peaks form, then add the caster sugar, whisk again, then fold into the batter.
Butter an aebleskiver pan and set over a medium-high heat. Spoon 1 tbsp batter into each hole and allow to cook and set for about 1 min. Use a skewer or pointed palette knife to flip the pancakes around forty degrees, then add a bit more batter, allow to set and flip again, cooking and rotating until you have a golden puffed pancake ball. Alternatively, drop spoonfuls of batter into a buttered non-stick frying pan and cook for several mins on each side. Dust with icing sugar and serve hot.