If using a hand mixer affix the beaters, if using a stand mixer affix the paddle attachment and then beat your softened butter a few times to ensure it is adequately soft, if it no longer sticks around the beater/paddle attachment then it is ready.
Tip in your sifted icing (confectioner's) sugar and beat, starting on a low setting and then moving up to medium-high, until smooth. This can take 1-2 minutes. Wipe down your bowl intermittently with your spatula to ensure everything is mixed equally.
Add your orange juice and zest and beat in just until incorporated.
Sift your flour and salt together, then add to your beaten butter and sugar mixture and beat on a low setting until just incorporated. The mixture will be lumpy and doughy.
Add your chopped cranberries and chopped pistachios, mix them in with your hands, squidging them into the dough, but be careful not to overwork the dough or your shortbread will be tough.
Tip the shortbread dough out onto your work surface and then bring it together into a ball, but do not knead it. Roll the dough out into a sausage shape 21 centimetres long, you may find it easier to add a little flour to your work surface if the dough sticks. Make sure the ends are nice and flat.
Wrap your shortbread sausage in cling film (plastic wrap) and refrigerate for at least an hour, this resets the butter and ensures your shortbread does not flatten and spread when baking. The dough will keep for up to 3 days refrigerated if necessary, or an can be frozen and then defrosted before baking.
Heat your oven to 150°C Fan/170°C/340°F/Gas mark 3.
Line your baking sheet with a sheet of greaseproof (parchment) paper.
Unwrap your shortbread sausage and cut it in half and then half again, then cut each quarter into 3, giving you 12 cookies in total.
Place your cookies onto your baking tray. If they have warmed up a little pop them back in the fridge to reset, baking when they are stone cold is vital to ensure they keep their shape.
Bake for 25-30 minutes, until the rim of the shortbread is just starting to turn golden and the base is also lightly golden.
Leave to cool on the baking sheet for 10 minutes and then remove the cookies to a cooling rack to fully cool before decorating.