Peel the sweet potatoes and cut into 1" cubes. Add to a pot of boiling water and boil until soft, about 12 minutes.
Heat the mashed sweet potato in a pot to remove excess moisture. If there are still any lumps in the mashed potato, mash it again until smooth. Allow the potato to cool.
In a large bowl, mix the mashed potato with half of the flour, and the salt, and mix well. Add more flour, a little at a time, to get a thick dough consistency. You may not need all of the flour. Knead the dough well to ensure the flour is all incorporated.
Divide the dough into four equal pieces and on a lightly floured surface, roll each piece into a long thin strip - about ½ inch thickness. Make a cut every 3cm, to create equal bite-sized pieces.
Lightly dust each piece with flour, and press on them gently with a fork to create small indentation marks. Store in the fridge until ready to cook.
For the creamy spinach sauce
Heat the oil in a pan over medium heat. Add the onion and cook for a few minutes until translucent, then add the garlic and cook, stirring, for a further minute. Add the spinach and cook until it wilts.
Transfer the spinach mixture, along with the cream and nutmeg, to a food processor or blender and whiz until smooth. Taste and season well.
Cook the gnocchi
When you’re ready to cook the gnocchi, but a large pan of salted water onto the boil. Add the gnocchi pieces, then turn the water down to a simmer.
Cook for a few minutes until they float. Remove with a slotted spoon and serve with the spinach sauce.