For the pasta, pour the flour into a mound onto a flat surface and make a well in the centre. Crack the eggs into the well and gradually mix with either a blunt knife or your hands. When the dough has become a thick paste use your hands to incorporate more of the flour.
You can sieve any remaining flour and use the sifted flour while you knead the dough to stop it sticking to the surface and to your hands, but be careful not to make the dough too dry. Knead until well blended and the dough is soft and flexible. Don't worry if you haven't used up all the flour.
Leave the pasta to rest for about 20 minutes with a bowl inverted over it or leave it covered in cling film. You can sieve any leftover flour again and save this flour for rolling out the pasta.
Meanwhile, for the filling, in a clean bowl, mix the spinach, ricotta, parmesan and nutmeg well, and season with salt and freshly ground black pepper.
Divide the fresh pasta into four and keep three portions under a bowl while you roll and stuff one quarter. This prevents the pasta from drying out. Roll out the pasta into a long, wide strip about 1mm in thickness, either by hand or using a machine. When you can see your hand through it, it is ready for stuffing. Cut the strip in half.
Place teaspoons of the filling in a line down the centre of one of the strips about 5cm/2in apart. Place the other strip directly on top. Press the air out from around the filling by pushing down the pasta around them sealing them in. Now take a small wine glass or round cutter measuring about 7cm/3in across and cut out circles of pasta around each mound of filling.
They can be cooked straight away or stored in fine semolina for up to two hours. You can also freeze them at this stage and then cook them from frozen when you are ready.
To cook, bring a large pan of salted water to the boil and gently lower in the tortellini. Cook for about four minutes or until the pasta is soft but not floppy.
While the pasta is cooking make the sauce. Preheat the grill to hot.
Toast the pine nuts under the grill or in a dry frying pan. They are quick to brown so don't take your eyes off them.
Put the pine nuts, sage leaves and butter into a frying pan and melt the butter taking care not to burn it. Add about a tablespoon of the pasta water and stir together to emulsify the sauce. Remove from the heat.
When the pasta is done, drain it and toss with the sauce in the frying pan. Serve immediately sprinkled with parmesan.