Mix together the flour, pumpkin spice and sugar in a large bowl.
Add the cold, diced butter and rub it in using your fingertips until it resembles fine breadcrumbs and no lumps of butter remain.
Use your hands to bring the dough together into a ball. Don't knead it, just handle it enough so that it forms a smooth dough.
Form the dough into a log about 5-7cm thick - use your hands and roll it on a surface to get it as even as possible. If needed you can dust the surface with a little flour.
Wrap the log in a piece of baking parchment, twisting the ends tightly to form a cracker shape. Refrigerate for 1-2 hours until firm.
Meanwhile, preheat the oven to 180°C/160°C fan/350°F/gas mark 4 and line two baking sheets with baking parchment.
Use a very sharp knife to slice the log into approx 5mm thick slices. (If the dough has become too firm to slice, let it sit out at room temperature for about half an hour before slicing it).
Place the cookie slices slightly spaced apart on the baking sheets and bake for 20-25 minutes until lightly browned around the edges and on the underside.
Allow to cool on the tray for 5 minutes then carefully transfer them to a wire rack to cool completely. Once cold store in an airtight container.