When buying Parmesan or Parmigiano, go for Reggiano. This is the best - anything that does not call itself Reggiano is not true Parmesan. Pickle the tomatoes one week in advance.
Pre-heat the oven to 110°C/gas mark ¼ or its lowest possible temperature. Halve the plum tomatoes, lay them on the grill rack and put them in the very cool oven. Leave them overnight so that they dry out. Bring to the boil the two vinegars, sugar, rosemary and thyme, then leave it to c