Cook the pasta in a large pan of salted boiling water until al dente. Gently fry the onion in the oil over a medium heat for about 4 minutes, until soft and translucent. Add the garlic to the onion, cook for 1 minute, then add the chopped tomatoes, tomato purée and cayenne pepper, and crumble in the stock cube. Stir everything together and simmer for 5 to 10 minutes, then stir the olives into the sauce and simmer for a further 2 to 3 minutes. Just before serving, sprinkle the Parmesan over the sauce and stir in torn pieces of the mozzarella. Scatter over the spinach. Drain the pasta and gently mix it into the sauce. The moisture and heat from the pasta will wilt the spinach. Add a splash of the pasta water to loosen the sauce, if needed. Season to taste with salt and pepper, then serve with a drizzle of extra virgin olive oil and a little extra grated Parmesan on top. TipOlives should always be bought with their stones still in, as they will be much tastier. We often keep a few spare jars in the cupboard for unexpected visitors (they are great with toasted bread and olive oil as an antipasto). To remove the stones from your olives, squash them with the heel of your hand and the stone will pop out!