Turn the oven on to 180°C.
Cut the tomatoes in half, then place them in a large baking tray, cut-side facing upwards.
Peel and cut the onion into 6 wedges. Chop the carrot into 2 cm pieces. Chop the courgette into 3 cm pieces. Arrange these around the tomatoes, together with the garlic cloves (unpeeled, but slightly squashed).
Add the thyme leaves. Drizzle with the oil and vinegar, then season with salt and pepper. Toss well, then bake for 25-30 minutes, until the vegetables have softened. Set aside in a bowl, if you're not making the soup immediately.
Discard the skin of the garlic cloves. Transfer the veggies to a saucepan, including the cooking jus. Add the stock and bring the boil. Cook for 5 minutes and add the basil.
Using a stick-blender, whiz the soup until you get a smooth texture. Add more stock if the soup is too thick and reheat.
Serve warm with a squeeze of lemon juice and freshly ground pepper.