Heat the oven to 220C/fan 200C/gas 7. Butter a large baking sheet. In a large bowl, mix together the flour, baking powder and salt. Rub in the butter with the oil, until the mixture resembles fine crumbs, then add the tomatoes, cheese and olives. Make a well in the centre, pour in the milk and mix with a knife, using a cutting movement, until it becomes a soft ‘stickyish’ dough. (Use all the milk – it helps give a light texture.) Don’t overhandle the dough.