Heat a tablespoon of olive oil in a large non-stick pan, over a medium heat.
Using an 8cm/3 inch cooking ring, place it on the pan then fill it with the sweet potato mixture, fill the ring to just over halfway. Press down firmly on the rosti, using the spoon.
Leave to cook for about 2 minutes then remove the ring. Press down on the rosti with a spatula and cook for another 2 minutes. Flip the rosti, press down again and cook for about 2 minutes. Continue for the remaining mixture. You should have 8 rosti.