Preheat the oven to 170°C (325°F/Gas 3). Remove the excess sinew and fat from the duck breasts. Score the skin with a sharp knife and season with salt and pepper. Heat a large ovenproof frying pan over medium heat. Sear the duck, skin-side down, until golden, then place in the oven and roast for 6 minutes. Rest in a warm place for 5 minutes. Using a sharp knife, slice each breast lengthways into thin 2 mm (1/16 inch) thick strips. Arrange the slices, overlapping, then roll into a cylinder. Serve immediately.