Put the flour, semolina, eggs and olive oil in a bowl with a little salt. Knead with the dough hooks of a hand mixer. Add flour or a little water to make a firm dough. Knead by hand until the dough is smooth.
Wrap the dough in foil and chill for at least 30 minutes in the fridge.
Wash the spinach and blanch in boiling salted water for 1-2 minutes. Drain, rinse in cold water and drain well, pressing out all the liquid. Finely chop the spinach.
Peel and finely chop the onion and garlic.
Fry for 3-5 minutes in the hot butter over a medium heat until softened. Add the onions to the spinach.
Add Parmesan and ricotta to the spinach and stir.
Grate some nutmeg into the filling.
Season the filling with salt and pepper to taste.
Roll out the dough on a floured surface into thin strips, about 10cm wide.
Whisk the egg and brush over the dought. Put the filling in a piping bag and squeeze onto the dough.
Repeat with all the dough sheets.
Roll out the filled dough sheets lengthwise.
Using the handle of a spoon, press out the ravioli every 3cm along the dough.
Cut and press the ends well to seal. Bring plenty of salted water to the boil in a large pan and cook the ravioli for 3-5 minutes. Remove with a slotted spoon, drain and serve in a little butter.