To make the dough, prepare the work surface. Sift the flour, make a well in the middle and crack the eggs in.
Use a fork to beat the eggs well, gradually adding flour from the edges.
Use your hands to knead it very well into a dough that is smooth, elastic and does not stick to the hands.
Cover the dough with a kitchen towel, and leave it to rest for at least 30 minutes.
In the meantime, make the filling.
Add the frozen spinach nests to a pot, cover with water, and bring to a boil on a high heat.
Leave the spinach to cook until completely thawed.
Drain the water, and squeeze the excess water well.
Chop the spinach well and add it to a bowl together with the ricotta, grated parmesan, salt and pepper and mix well to combine.
Once the dough has rested, divide it into 3 parts.
Flour each dough roll well, and roll it lightly with a rolling pin.
Starting with the widest setting ( lowest number) on the pasta machine, feed each dough roll through the machine, gradually reducing the thickness until you reach setting 7.
Lay the pasta sheet on a floured surface, and place teaspoons of the filling in the middle of the sheet leaving about 4-5 cm between each mound of filling.
Fold the pasta sheet in half, and press gently around each mound of filling to remove any trapped air.
Seal the edges well, then use a ravioli cutter or a knife to cut out squares.
Transfer the ravioli to a floured surface in a single layer until all the filling and dough have been used up.
Bring a pot of salted water to the boil, add the ravioli and cook them for 3-4 minutes or until they float and the pasta is tender.
To make the sauce, add the butter to a large enough frying pan, and allow it to melt on a medium heat.
Leave it to simmer for 2-3 minutes until it turns slightly golden and nutty, then add the fresh sage leaves and allow them to infuse the butter for 1-2 minutes or until they look slightly crisp.
Transfer the ravioli to the pan together with 2 tablespoons of the water they cooked in, and swirl them around to be coated in sauce well.
Serve with plenty of parmesan.