To make the ravioli dough, make a crater with the flour on your tabletop. Add the eggs to the center of the flour crater. Partially incorporate the flour into the eggs with a fork. Then knead the flour and eggs together to form dough. Knead until the dough is thoroughly worked together, approximately 4 to 5 minutes. Reserve until the raviolis are ready to be assembled.

In a pot of boiling water, cook the spinach with half of the salt until tender. Remove the spinach from the boiling water and let cool for 2 to 3 minutes. Squeeze out the water from the spinach and chop it up roughly. In a mixing bowl, combine chopped spinach, ricotta, egg, heavy cream, and 4 tablespoons Parmigiano Reggiano. Season with the nutmeg, remaining salt, and black pepper.

To make the sauce, melt the butter in a saucepot. Simmer the nutmeg and sage in the butter for 1 minute. Reserve until the raviolis are cooked.

To assemble the raviolis, cut the dough into 4 pieces. Roll out each piece to form a thin layer (about 1/8 inch) of dough. Place 1 spoonful of filling onto 1 sheet of dough 1/2 inch from the edge. Continue to place spoonfuls of filling along the dough 1-inch from each other.

Place 1 of the other pieces of rolled out dough on top of the piece with the filling on it. Pinch the dough around the filling to form the ravioli. Use a cookie cutter or a knife to cut out the raviolis. Pinch the edges of each ravioli with the tines of a fork. Set aside each ravioli on a plate lightly dusted with flour. Do not stack the raviolis, because they will stick together.

When you are ready to cook the raviolis, add them to boiling water. When the raviolis float, about 2 to 3 minutes, they are finished cooking. Serve each portion with the sage butter and sprinkle 1 tablespoon of grated Parmigiano-Reggiano over each serving.