01 - On a clean work surface, mound 2 cups of all-purpose flour and create a well in the center. Add 3 large eggs and 1/2 teaspoon fine sea salt to the well. Gradually incorporate the flour into the eggs using a fork, then knead by hand for 8-10 minutes until a smooth dough forms. Wrap the dough in plastic wrap and allow it to rest for 30 minutes.
02 - Steam or sauté 10 ounces of fresh spinach until wilted. Let the spinach cool, then squeeze out any excess water and chop it finely. In a medium bowl, combine the chopped spinach with 1 cup of drained ricotta cheese, 1/2 cup of grated Parmesan cheese, 1 large egg yolk, 1/4 teaspoon freshly grated nutmeg, 1/2 teaspoon salt, and 1/4 teaspoon black pepper. Mix until all ingredients are well combined.
03 - Divide the rested pasta dough in half. Using a rolling pin or pasta machine, roll each piece of dough into thin sheets, approximately 1/16 inch (2 mm) thick. Keep the rolled dough sheets covered with a clean kitchen towel or plastic wrap to prevent them from drying out.
04 - Place teaspoons of the prepared filling about 1 inch (2.5 cm) apart on one sheet of rolled pasta dough. Lightly moisten the edges of the dough sheet with water. Carefully place the second sheet of dough over the filling. Press down around each mound of filling to seal the ravioli and press out any air pockets. Use a sharp knife or a pasta cutter to cut the dough into individual ravioli squares. Ensure the edges are firmly sealed.
05 - Bring a large pot of generously salted water to a rolling boil. Carefully add the ravioli to the boiling water in batches, ensuring not to overcrowd the pot. Cook for 3-4 minutes, or until the ravioli float to the surface. Remove the cooked ravioli from the water using a slotted spoon.
06 - In a large skillet, melt 4 tablespoons of unsalted butter over medium heat. Add 8-10 fresh sage leaves to the melted butter. Cook, swirling the pan occasionally, until the butter turns a golden brown color and becomes fragrant, about 2-3 minutes. Season the sauce with salt and pepper to taste.
07 - Gently add the cooked ravioli to the skillet with the sage butter sauce. Toss carefully to coat the ravioli evenly. Plate the ravioli and garnish with freshly grated Parmesan cheese before serving.