Mix the butter, sugar and vanilla extract with a wooden spoon. stir in the flour, then tip in the pistachios and cranberries - you might need to get your hands in at this stage to bring the mix together as a dough. Halve the dough and shape each half into a log about 5cm across. Wrap in cling film, then chill for 1 hr or freeze for up to 3 months.
Heat oven to 180C/160C fan/gas 4. slice the logs into 1cm-thick rounds, place on a baking tray lined with baking parchment and bake for 12-15 mins. Cool completely on the tray.