Cook the spinach in boiling salted water for a few minutes. Drain it very well, pressing out the water. Cool, then chop it up fine and put in a bowl. Add the ricotta, a good grating of nutmeg, the parmesan and egg, mixing it all well together. Taste for salt and pepper.
Preheat the oven to 180°C (350°F/Gas 4).
Heat 3 tablespoons of olive oil in a saucepan with the squashed garlic. Add the tomatoes and basil and season with salt and a little pepper. Swirl about 125 ml (4 fl oz/½ cup) of water around in the tomato tin and add that too. Simmer for 5 minutes or so. If there are still big bits of tomato, crush them with a fork or potato masher. Remove from the heat.
Drizzle the remaining 2 tablespoons of olive oil into an oval baking dish, roughly 26 x 14 cm (10½ x 5½ inches). Spoon about one-third of the tomato sauce over the bottom of the dish. Take a tablespoon of the spinach mix and edge it off gently with another spoon onto the tomato sauce in the dish. Continue with the remaining spinach mix, resting the balls in compact rows. You will have about 16 balls. Dollop the rest of the tomato sauce over the balls. It’s best if most of them are covered, at least in part.
Bake for 20-25 minutes, until a bit golden here and there. Serve warm, scattered with parmesan.