Peel and cut the potatoes into chunks. Boil them in a large pot of salted water until tender, about 15-20 minutes.
Drain the potatoes and let them cool slightly. Mash them until smooth or use a potato ricer for a finer texture.
On a clean surface, combine the mashed potatoes, flour, egg, salt, and nutmeg (if using). Mix until the dough comes together.
Gently knead the dough until smooth. Be careful not to overwork it, as this can make the gnocchi dense.
Divide the dough into 4 portions. Roll each portion into a long, thin rope, about 1/2 inch in diameter.
Cut the ropes into small pieces, about 1 inch long.
To shape the gnocchi, use the back of a fork to press gently on each piece, creating a small indentation and ridges. This helps the sauce cling to the gnocchi.
Bring a large pot of salted water to a boil. Gently drop the gnocchi into the boiling water. Cook in batches if necessary.
When the gnocchi rise to the surface, they are done. Remove them with a slotted spoon and set aside.
In a large skillet, melt the butter over medium heat. Add the sage and cook for 1-2 minutes until fragrant.
Add the cooked gnocchi to the skillet and toss to coat in the butter and sage. Cook for an additional 2-3 minutes until lightly golden.
Sprinkle with grated Parmesan cheese and season with salt and pepper to taste.
Enjoy your meal!