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.

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.

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.

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.

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.