Arrange the thinly sliced naartjie peel in the airfryer basket and roast at 180°C for 10 minutes; if you don't have an airfryer, you can roast it the same way in the oven.

Transfer the roasted peel to a pot and simmer with the erythritol, water and lemon juice over low heat for 20 minutes, until it thickens.

Pour the hot mixture into a sterile jar and let it cool at room temperature for 30 minutes.