Mix the flour and salt in a bowl. Add the yeast, water and oil, mix with a wooden spoon. Knead to form a soft, smooth dough. Cover and leave to rise at room temperature for approx. 1 hr. until doubled in size.
Heat the oil in a pan. Sauté the onion and garlic, add the tomato puree and cook briefly. Add the tomatoes, rosemary, sugar and salt, bring to the boil. Simmer the sauce over a medium heat for approx. 20 mins., stirring occasionally, leave to cool.
To top the pizzas
Divide the dough in half, shape into 2 balls, flatten both pieces a little, roll out into circles on a lightly floured surface, transfer each pizza base to a prepared tray. Spread the tomato sauce over both pizza bases, leaving approx. 1.5 cm free around the edges. Top with the mozzarella, chorizo and chilli pepper.
Approx. 20 mins. on the bottom shelf of an oven preheated to 240°C. Bake the second pizza in exactly the same way.