Preheat the oven to 180°C (fan)/350°F/Gas Mark 5.
In a large saucepan, add the spinach, a drizzle of olive oil, half the nutmeg (¼ teaspoon), a pinch of salt and pepper. Cover the pan and leave the spinach to sweat and wilt down, stirring occasionally. Pop in a bowl and set aside.
In a large pan fry the onion until soft and golden. Add the garlic and fry for a further minute.
Add the plum tomatoes and break them up with a spoon (or with your hands as you add them!).
Add the sugar, lemon zest and a few basil leaves. Simmer for around 20 minutes until the sauce has thickened. Add salt and pepper, try the sauce and add more until you get the desired seasoning.
While the spinach is sweating and the tomato sauce is simmering, make the 'ricotta'.