Wash the sweet potatoes. Peel.
Cut into fries / chips. Put into a large bowl.
Add the 1 tablespoon of oil to the bowl and just using your clean hands, toss well until all surfaces of the potato are coated. (Tip! first have air basket pulled out and beside you, ready to receive the potatoes, because your hands will be oily.)
Cook (no need to pre-heat machine) at 160 C (320 F) for 15 minutes.
Take out the fries and tip them back into the bowl you have been using. Toss them in there briefly and gently using a large spoon, or just by tossing the bowl.
Transfer fries back into fryer basket. Place back into machine, raise temperature on the machine to 180 C (350 F), and cook for another 5 minutes.
Take out the fries and tip them back into the bowl you have been using. Toss them in there using a large spoon. (At this point, a few might look just about done, but once you toss them you'll see that there's loads that aren't quite as far along.)
Transfer fries back into fryer basket. Leave temperature unchanged. Roast for a final 5 minutes.
Serve piping hot.