In a large bowl, combine the flour and salt. Add the eggs and olive oil, then mix until a dough forms.
Knead the dough for 8–10 minutes until smooth and elastic.
Wrap the dough tightly and let it rest for 30 minutes at room temperature.
Cook the spinach in a dry skillet for 2–3 minutes until wilted. Let it cool, then squeeze out all excess moisture and chop finely.
In a bowl, combine the spinach, ricotta, Parmesan, egg yolk, nutmeg, salt, pepper, and garlic (if using). Mix until smooth.
Roll the dough into thin sheets using a pasta machine or rolling pin.
Place small spoonfuls of filling onto one sheet, leaving about 2 inches between each mound.
Brush water around each mound, cover with another pasta sheet, and press firmly to remove air pockets.
Cut the ravioli using a ravioli cutter or stamp.
Bring a large pot of salted water to a gentle boil.
Cook the ravioli for 3–4 minutes, or until they float to the surface.
Meanwhile, melt the butter in a skillet and cook the sage leaves until fragrant.
Transfer the ravioli to the skillet and gently toss to coat.
Sprinkle with Parmesan cheese and chopped parsley before serving.