Preheat your oven or air fryer to 400°F (200°C). Pierce the sweet potatoes with a fork a few times and roast them on a baking sheet for about 45-50 minutes until soft. Allow them to cool for a few minutes and then scoop out the flesh and mash it until smooth.
In a large mixing bowl, combine the mashed sweet potatoes, ricotta cheese, egg, Parmesan, salt, and nutmeg. Gradually add the flour, starting with 1 ½ cups, mixing until a soft, slightly sticky dough forms.
Flour a clean surface and place your dough. With a rolling pin, roll the dough into a rectangle shape that is about ½-inch thick and about 4 inches wide. Cut the dough into 4 even strips. Cut each of the strips into 1-inch pieces. If desired, use a fork to create ridges for a more traditional look. (*If the dough feels too sticky, even on the floured surface and floured rolling pin, you may want to add ¼ cup more flour at a time to it until it can be rolled out. Do not add so much that it feels tough and dense, it should still feel springy.)
Bring a large pot of salted water to a boil. Cook the gnocchi until they float to the surface, about 2-3 minutes. Remove with a slotted spoon and transfer to a plate.
In a large skillet over medium heat, melt the butter. Add the sage leaves and garlic. Cook until the butter turns golden brown and has little browned bits in it, about 4-5 minutes. Be careful not to burn it.
Add the cooked gnocchi to the skillet and coat in the sauce. Cook for 1-2 minutes to let the gnocchi absorb the flavors and get a little bit more color to them. Season with salt and pepper to taste. Serve right away with some extra Parmesan on top.
