Preheat the oven to 200°C/Gas 6.
Arrange the tomatoes on a roasting tray. Halve any large tomatoes.
Quarter one of the onions. Trim and peel the quarters. Tuck the pieces amongst the tomatoes. Drizzle with just enough oil to gloss.
Roast for 30 mins, or till it’s all meltingly tender.
Halve the other onion. Peel. Cut into 2-3cm thick slices. Wash or peel your carrot. Finely dice. Finely dice the celery. Set a saucepan over high heat. Add a gloss of oil. Stir in your veg. Let it cook till just softened. Add the boiling water. Simmer till your tomatoes are roasted.
Tumble the tomatoes, onion and any juice into a food processer or blender. Add 1cm of peeled ginger. Whizz till puréed. Add the tamari. Strain your stock. Add half of the stock to the blender. Taste. Add more tamari to taste, and more stock if needed.
Pass through a sieve if you want a smooth soup. Heat through and serve in warmed bowls.