– Grease and line a 20cm (8 inch) cake tin. – Heat the oven to 160°C/140°C fan (315°F).
– In a food processor, grind the pistachios with the flour to a slightly sandy powder. Tip out and set to one side.
– Put the butter and sugar in the food processor and whiz to a paste. Add all the remaining ingredients, including the pistachio flour, and whiz again.
– Scrape the batter into the tin and rap on the work surface a few times to level. – Bake for up to an hour, until the top is golden and springy and a skewer in the middle comes out clean.
Leave in the tin for 10 minutes before turning out onto a rack to cool completely before icing. For the icing, mix the icing sugar and lemon juice to make a slick of glossy white.
Pile into the middle of the cake and encourage it to ooze languidly towards the edges. This cake keeps well in a tin for a few days and the flavour only gets better, but the icing looks at its sleekest when fresh.
– Alternatives: instead of the coriander seeds, you can use the ground seeds of 8 green cardamom pods. You can also add a splash of rose water to the icing, if you like.