Preheat the oven to 200°C (180°C fan oven) Gas Mark 6.
Unroll the pastry on top of a baking sheet, and slice a 1cm ribbon of pastry from one end, and one side. Score a 1cm border around the new pastry edges, then prick all over the middle with a fork. Mash together the tomato purée, olive oil, dried oregano and 1 tbsp water with some pepper, then spread over the inside of the border. Use the two strips of pastry you cut off to make a cross that sits across the middle of the pastry. Bake for 10 minutes.
Scatter each quarter with different pizza toppings – or get your family to each make their own quarter using their favourite flavours.
Sprinkle mozzarella all over the top, then bake for a further 15 minutes until the pastry is golden and crisp. Serve straightaway, scattering some basil leaves over the Parma ham, if using.