1. Cook the Potatoes: Wash and boil the potatoes with their skins until fork-tender. Drain, allow them to cool slightly, then peel.
2. Mash the Potatoes: Mash the potatoes thoroughly while still warm until smooth. Let them cool enough to handle.
3. Prepare the Dough: Place the mashed potatoes on a clean work surface. Add the egg, salt, pepper, and nutmeg. Gradually incorporate the flour until a soft dough forms. Avoid overworking it.
4. Shape the Gnocchi: Divide the dough into portions. Roll each portion into a long rope about 2 cm thick, then cut into small pillow-shaped pieces. Gently press each piece with a fork to create ridges.
5. Prepare the Sauce: Heat olive oil in a saucepan. Add the onion and cook until softened. Stir in the garlic, crushed tomatoes, tomato paste, oregano, salt, pepper, and water.
6. Simmer the Sauce: Cook over low heat for 15–20 minutes, stirring occasionally, until the sauce thickens. Add fresh parsley or basil.
7. Cook the Gnocchi: Bring a large pot of salted water to a gentle boil. Add the gnocchi in batches. When they float to the surface, cook for another 30–60 seconds, then remove with a slotted spoon.
8. Combine and Serve: Toss the cooked gnocchi gently with the tomato sauce. Serve hot with grated cheese and fresh herbs.