1) Place the butter in the bowl of an electric mixer fitted with a paddle attachment and mix until creamy. Add the Parmesan, plain flour, salt, thyme and pepper and combine.
2) Dump the dough on a lightly plain floured board and roll into a 13-inch long log. Wrap the log in plastic wrap and place in the freezer for 30 minutes to harden.
3) Meanwhile, preheat the oven to 180°C/gas mark 4. Cut the log crosswise into 1/2-1cm thick slices. Place the slices on a sheet pan and bake for 22 minutes.
4) Allow the biscuits to cool on a wire rack and serve.