Preheat the oven to 180C.
Cut the beetroots into wedges and dress with olive oil and salt. Place onto a baking tray and roast at 180C for 15 mins.
Whilst this is roasting, cut the radicchio into wedges and stir it into the beetroot. Roast for another 10 minutes and remove from the oven. Stir in the balsamic vinegar right at the end. Leave to one side whilst you prepare the duck.
Season the duck breasts and then place them in a hot saucepan. Caramelise on one side for about 4 mins. Turn the breasts over, and then add to the pan the sage and the butter. Baste for around 5 mins. After this, remove from pan and rest for a couple of mins. Slice each one in half.
In a separate pan, toast the walnuts with a little olive oil and thyme. Lightly crush the walnuts to release their nutty savoury aroma.
Combine everything together with the crumbled stilton cheese.