Coat the bottom of a large sautéing pan with olive oil and 3 cloves of garlic that has been crushed and left with the peel on.
Heat until relatively hot but not emitting smoke. Add spinach, and adjust to taste with salt. Allow to cook for approximately 5 minutes, until cooked through and tender.
Remove from heat, place on top of paper towels to cool off and release excess liquids. Once cooled, squeeze spinach in another paper towel to absorb as much excess liquids as possible.
Once spinach has cooled off, chop coarsely in large pieces, and add in as much ricotta as you wish, using up to 400g in total. Season mixture to taste with salt, freshly ground black pepper and nutmeg.
Sift the flour on the wooden board and hollow the center. Break the eggs and pour them in the hollow one by one.
Using a fork, beat the eggs together. Gently bring some of the flour into the egg mix. Continue drawing flour into the eggs a little at a the time until all the flour is absorbed.
Use your hands to obtain a uniform mixture, knead the pasta, pushing with the palm of your hands, until the dough feels smooth and firm.
Make a round, smooth ball and place it on a plate. Cover with a moistened cloth or a plastic wrap, and let the dough settle in a fresh place for 30 minutes to 1 hour.
Use the minimum flour necessary, just enough to prevent the dough from sticking to your hands while working.
Cut the dough in rectangles. Boil the pieces of pasta in salted boiling water for a few minutes, adding a few drops of olive oil to avoid having the pasta stick together.
Place the pasta sheet out flat, place spinach filling into the middle (not too much otherwise the filling will escape from the rolled pasta).
Roll the pasta up, to have the filling in the middle, and seal the edges of the pasta by slightly dampening the pasta on one side.
Repeat until you have filled and rolled all of the rectangular pieces of pasta.
Place all of the rolls into a deep baking dish, and proceed as indicated below.
Crush the peeled tomatoes with your hands or a fork, and put in a pan with the garlic, the basil and salt.
Let it simmer gently until thickened. Turn off the fire, add the extra virgin olive oil to taste.
Cover the filled cannelloni with tomato sauce and a sprinkling of freshly grated Parmesan cheese. Place in preheated oven (200C), and allow to cook for about 10 minutes, to form a crunchy top on the pasta, and to lightly melt the cheese.