Heat oven to 200C/fan 180C/gas 6. Halve the tomatoes and put them, cut side up, in a single layer in a large ovenproof dish or baking tray. Tuck a sliver of garlic into each tomato half and scatter over thyme leaves. Drizzle with the oil, season generously, then bake for 30-40 mins or until the tomatoes are soft and juicy. Leave to cool. Can be roasted and chilled up to 3 days ahead. Bring to room temperature before serving.
To serve, carefully lift the tomatoes onto a serving plate and pour over some of the juices from the roasting dish. Whisk together the honey, vinegar, mustard and a little seasoning to make a dressing, drizzle over the tomatoes and scatter with a few more thyme leaves.