1. Pre-heat the oven to 210°C.
2. In a free standing electric mixer with a whisk attachment, whisk the egg and sugar until it has tripled in volume and the ribbon stage is reached; when you lift out the whisk and draw a figure of 8 with the falling batter, it should sit on the surface of the mixture for 3 seconds or so.
3. Sift the flour, pistachios and cardamom onto a piece of baking paper to blend, then sprinkle over the surface of the mixture and fold in. when just about folded in, add the butter and fold to a smooth batter, trying not to knock out any air.
4. Put the mixture into a piping bag and put it into the fridge for 2-4 hours. Pipe the mixture into the prepared madeleine tins and bake in the preheated oven for 7-9 minutes, or until the madeleines spring back when lightly prodded.
5. Remove from the tin immediately by standing the tin on its end and giving it a sharp tap on the counter.
6. Set the madeleines on a wire rack to cool completely.
7. For a dipping sauce, melt the white chocolate in a heatproof bowl, over a saucepan of simmering water, making sure the bowl doesn’t touch the water. Add the cream to the chocolate and mix together.