Brush off any loose dirt from the Jerusalem artichoke tubers, then soak in cold water for at least 20 minutes
Drain and clean the tubers using a vegetable brush
Trim any roots or soft parts from the tubers
Cut the tubers in half lengthways
Put them in a bowl along with the garlic cloves and rosemary, then dress with the oil and plenty of salt and pepper
Spread out on a baking sheet so you have a single layer of tubers, skin side up
Preheat your oven or airfryer to 180C (175c for fan assisted)
Put the tray in the oven and leave for 25 to 30 minutes
Take the tray out and turn all the tubers.
Turn the heat up to 200C (190 fan assisted) and return the tray to the oven for 20 minutes
Drain the tubers on kitchen paper and serve