1. Preheat the oven to 180℃ Fan and line two baking sheets with parchment paper.
2. In a large bowl, stir the flour, icing sugar and 50g of ground up pistachio nuts together. Add in the butter and mix with a hand mixer or in a stand mixer with paddle attachment on low-medium speed until blended well. The dough will look crumbly and soft but should stick together when squeezed in your hands.
3. Place a sheet of grease proof paper on your worktop and sprinkle with some flour. Form the dough into a ball and place in the middle of the paper.
4. Place another piece of paper for the top, sprinkling a little more flour on top of the dough to prevent sticking, and roll the dough to approximately 1/2 of an inch thick. 
5. Use a pizza roller or shark knife to cut the dough into sticks (refer to video for reference). Continue re-rolling the dough until it is all used.
6. Place on the lined tray and bake in the middle of the oven for 10-12 minutes, or until the edges of the shortbread sticks are slightly golden.
7. Remove from the oven and allow to cool on the tray for 10 minutes before transferring to a cooling rack. 

Method (chocolate decoration)

1. Lay the shortbread sticks on some grease proof paper, giving them space for the chocolate tree decoration. Place the white chocolate into a bowl on top of a saucepan with boiling water, creating a bain-marie and allow the chocolate to fully melt. You can alternatively melt in the microwave in 20 second intervals.
2. Stir in a little drop of green food gel and stir to combine. Transfer the chocolate into a piping bag and snip off a small tip.
3. Use the chocolate to pipe a zig-zag pattern over the shortbread in a ‘tree shape’ (refer to video for example). Repeat for all the shortbread sticks.
4. While the chocolate is still wet, you can sprinkle over some more ground pistachio nuts (the remaining 10g). Alternatively, you could add some some festive sprinkles, cookie crumbles or chocolate chips. 
5. Allow to set in the fridge / freezer for 20 minutes, then serve and enjoy.