Mix the potatoes with the cornflour, oil and salt, spread onto a baking tray lined with baking paper.
Bake for approx. 20 mins. in the centre of an oven preheated to 220°C.
Place the raclette cheese in the raclette pans, top with the sweet potatoes and onion, sprinkle with rosemary. Melt under a raclette oven grill for approx. 8 mins.