Turn the oven on to 180°C.
Cut the tomatoes in half then place them in a large, shallow baking tray, cut-side facing upwards.
Peel, then cut the onion into thin wedges. Tuck them between the tomatoes together with the peeled garlic cloves. Drizzle with the oil and vinegar, then scatter with the spices and sugar (if used). Season with salt and pepper. Toss well, then bake for approx. 25 minutes until the vegetables have softened.
Transfer everything to a saucepan, including the cooking jus. Add the stock and bring the boil. Cook for 5 minutes then add the spinach, cook for another minutes or so, then turn off the heat, put a lid on and steam for 5 minutes. Add the herbs.
Using a stick blender, whiz the soup until you get a smooth texture.
Serve warm with a squeeze of lemon juice or dash of cider vinegar and freshly ground pepper.