Preheat oven to 150°C/300°F/Gas Mark 2. Place a cake rack on a baking tray and heat in oven for a few minutes. Cut the top and bottom off tomatoes, then slice them into ½ cm(¼ in) thick slices with a sharp knife.
Lay them on heated rack, sprinkle with good salt (Maldon is my favourite) and cracked pepper. If tomatoes aren’t too ripe, sprinkle with a little caster sugar, too.
Place in middle of the oven and leave for 1 hour, then check. They should have firmed up, at which point you can turn them over and leave for another hour before removing from the oven. If they start to brown, turn heat down a little.