Cut a large piece of baking paper and place on your work surface. Dust with plain flour.
Remove a chilled disk of dough from the fridge, take out of the bag and place onto the baking paper and dust with more plain flour.
Roll the dough out until it's about 2mm (1/16-inch) thick, dusting the top and underneath the dough with flour as needed to prevent it sticking to the paper too much. Cut out into 5cm (2-inch) circles. Remove the scraps around the edges and transfer the circles to a baking tray lined with baking paper. Chill for 15 minutes.
As the cut cookie dough is chilling, preheat the oven to 130°C (266°F). Use this time to also roll and cut circles from the second disc of dough. Place onto a second, lined baking tray. Use a small circular cutter (or the end of a piping tip) to cut a small circle from the centre of these cookies. Chill for 15 minutes as well.
Remove the chilled cookie circles from the fridge and bake for 25-35 minutes; the cookies should barely start to colour and should become crisp once cool (they'll stil lbe slightly pliable when hot). Allow to cool on a wire rack.
Re-roll the scraps, cut and bake as above, making sure that there's one plain circle per one 'doughnut shaped' circle so they can pair up when being sandwiched!
Take a plain circle cookie (without the hole) and spread a thin layer of the white chocolate ganache over the surface of the cookie. Take one of the cookies with the hole in the middle and sandwich it on top. Repeat with all your baked cookies!
Store in an airtight container for up to 5 days - they will soften a bit as they sit.