Stir salt into 1 ½ cups of flour. Sprinkle flour mixture over the sweet potato and fold to combine being careful not to overwork the dough. Add more flour as needed until you reach a sticky dough that can be formed into a loose ball using as little flour as possible.
Transfer dough onto a well-floured surface.
Portion dough into 5 inch round balls and roll each into 1 inch wide ropes. Cut the ropes into about ½ inch pieces. For the classic gnocchi shape (optional), slide each gnocchi over the tines of an upside down fork using your thumb to press it down the fork, optional.
Bring a large pot of water to a boil. Working in batches, drop each gnocchi into the boiling water. When the gnocchi floats to the top it's done (2 to 3 minutes). Remove with a slotted spoon and set on a paper towel.
Melt butter in a large saucepan over medium heat, then add garlic, sage, rosemary, and gnocchi. Cook until gnocchi is lightly browned, about 5 minutes (you may need to work in batches to cook all the gnocchi).
Remove pan from heat and transfer all gnocchi back into the pan.
Top with parmesan cheese and drizzle with cream stirring to coat.