Lemon and pistachio shortbread biscuits

Method

1. Put the pistachios in a dry frying pan over a medium heat and toast for 5 minutes until fragrant, then transfer to a food processor and whizz into a crumb. Pour out half and set aside for later, then add 90g of the icing sugar, the salt, both flours and lemon zest to the processor and pulse a few times to combine. Add the butter and pulse again to create a breadcrumb-like consistency.
2. Add the egg yolk and pulse again to bring everything together into a dough. You may need to add a small splash of cold water to help things along. Tip the dough onto a work surface and bring together, trying your best not to overwork the mixture. Wrap well and chill for at least 2 hours.
3. Line 2 large baking trays with baking paper. Unwrap the dough and roll it between 2 sheets of baking paper until it’s 5-7mm thick (work in batches if you need to). Use a cutter to cut out around 34 discs, transferring them to the lined trays as you work. Chill the trays in the fridge for 30 minutes.
4. Heat the oven to 160°C fan/gas 4. Bake the biscuits for 18-20 minutes until light golden, then leave to cool on the trays.
5. Meanwhile, put the remaining icing sugar in a bowl and add the lemon juice, 1 tsp at a time, until you reach a pouring consistency. Dip half of each biscuit in the icing, then sprinkle with the reserved pistachios. Return to the trays for another 20 minutes to set.