Half fill a medium saucepan with water. Bring to the boil. Add the chopped sweet potato to the boiling water and boil for 8 minutes.
Drain the sweet potatoes in a colander and allow to steam for five minutes. Add the sweet potatoes to a large bowl and mash with a potato masher or ricer. Get it nice and smooth.
Add the creme fraiche, nutritional yeast, salt and pepper and mix well. Add the flour half a cup at a time, mixing lightly between each addition. Don’t overmix or the Gnocchi will become tough.
Once all the flour is added, if the dough is still very sticky sprinkle with flour and cover the bowl with a tea towel - leave for a few minutes. The dough should be easy to handle and only slightly sticky.
Quarter the dough. Take one quarter and roll into a long even snake on a floured surface. Chop the snake every half inch so you’re left with around 15-20 little Gnocchi. Repeat with the other quarters of dough. You can set your gnocchi aside in a floured baking tray or you can roll each gnocchi down a floured fork to give it nice ridges. Either way, your gnocchi is now ready to boil.
Half fill the same pan that you boiled your potatoes in with salted water and bring to the boil. In batches of around 10, add the gnocchi to the boiling water using a slotted spoon. Once they’re cooked, they’ll bob to the surface of the water.
Remove the gnocchi from the water with a slotted spoon and repeat until all your gnocchi is cooked.
At this stage you can make the sauce and serve immediately, or you can cook the gnocchi and refrigerate or freeze for a later date.