There mightn't be a prettier version of shortbread than this. Flecked with specks of green pistachio and pink rose petals, it's easy to make yet gorgeously impressive. Dried rose petals can be found online or in speciality spice shops.
Mix together the flour, icing sugar and salt. Tip in the cubed butter, and rub together until mixture resembles fine breadcrumbs. Add the egg yolk and combine until a solid ball of dough is formed.
Work in the pistachios and rose petals. Roll dough into a log, approximately 3cm in diameter and 25cm long. Wrap in cling film and chill in the fridge for 2 hours, or up to 5 days if making ahead.
Preheat the oven to 170 C / Gas 3. Line a baking tray with baking parchment.
Once dough is chilled and solid, remove cling film. Slice into 5mm rounds and place on baking tray. Bake for 15 minutes, or until a light golden colour. Cool and store in an airtight container.