Preheat the oven to 150 C. If the tomatoes are especially juicy prick them with a fork before roasting.
Put all the tomatoes in a bowl, season with sea salt and black pepper and toss with the garlic. Spread out on a baking tray without overcrowding. Scatter over the thyme sprigs and drizzle over some olive oil.
Roast for 1- 1 1/2 hours, draining the juice halfway through cooking, until concentrated and dry.