Preheat the oven to 120°C/gas ½ and line a roasting dish with baking parchment.
Cut the tomatoes across in half and scoop out and discard the seeds. Cut each half across again in half. Place the bay leaves in the dish and sit the tomatoes in it. Drizzle with the 100 ml olive oil, season generously with salt and pepper, then place in the centre of the oven and cook for 1 ½-2 hours. You don’t want the tomatoes to colour at all, but to dry out a bit. They must still look a little plump, though, and not at all desiccated.
Heat a jar in the oven for 10 minutes with the tomatoes (removing any rubber seals), then place the tomatoes and bay leaves in the jar, pour in the cooking oil and juices, and top up with extra olive oil to the jar’s lip.
Seal and leave to cool at room temperature, then store in the fridge for up to 8 weeks. The tomatoes will be fine if kept covered with the oil. The oil may solidify when it is kept in the fridge, giving it a spotty look, but it will be fine if allowed to warm to room temperature.