Heat your oven to 200°C/Fan 180°C/Gas 6. Set a large roasting tin on the top shelf to warm. Finely chop the leaves from 1 rosemary sprig. Peel and finely chop 2 garlic cloves. Tip the rosemary and garlic into a pan with the polenta and a big pinch of salt and pepper. Whisk in 250 ml boiling water till thick and smooth. Pop in the fridge to set.
Quarter your tomatoes. Cut the peppers into 3-4 cm chunks, removing the seeds and stems. Tumble into the warmed tin with 1 tbsp oil. Season. Roast for 20 mins.
Halve, peel and chop your onion. Peel and chop the remaining garlic. Mix the onion, garlic and 2 tbsp balsamic in with the tomatoes. Roast for a further 5 mins.
Scoop the roasted veg into a blender or food processor. Blitz, trickling in the remaining boiling water, till it’s as thick or as thin as you like.
Pour the soup into a pan. Taste and add more salt and pepper if it needs it. Bring up to a gentle simmer. Dollop in little spoonfuls of the polenta mix to the soup, creating little dumplings. Simmer for a couple of mins to warm the polenta dumplings. Ladle into warm bowls to serve.
[Did you know?] Red peppers are a good source of vitamin C, while rosemary has anti-inflammatory properties.