Clean the squid and roughly chop the tentacles. In a saucepan, heat a drizzle of extra virgin olive oil with a clove of garlic, add the fresh baby spinach and the chopped tentacles and cook for a few minutes, until soft. Squeeze the water out of the spinach mixture, chop with a knife and put in a bowl. Add the finely grated Grana Padano, a few tablespoons of breadcrumbs, the eggs, salt and pepper, and mix well.
Fill ⅔ of each squid with the Grana Padano and spinach filling and use a skewer to close them. In a non-stick pan, heat a drizzle of olive oil with a clove of garlic, add the stuffed squid and brown on each side. Add the tomato purée, a few leaves of parsley, season with salt and pepper, and cook for 30 minutes over gentle heat, adding a ladleful or more of hot water, if necessary.
Serve the squid sliced with the tomato sauce and fresh parsley leaves.