Wash and prepare all the vegetables. Halve the onions and tomatoes, cut the peppers into large pieces and the carrots into smaller slices - so they have time to become tender.Slice the top off the head of garlic so the cloves are exposed.You should have a good 1.2 kg of vegetables - not counting the onions.
Spread all the vegetables out on a baking tray and drizzle generously with olive oil - including over the garlic.
Sprinkle over the dried herbs, season with salt and freshly ground pepper and toss everything together well.
Roast the vegetables in a preheated oven at 220°C, conventional oven (top and bottom heat), for about 45 minutes. The vegetables should be completely tender.
Tip all the vegetables into a blender. Squeeze the garlic cloves out of their skins into the blender, and add the fresh basil, the hot stock and the cream - start with 400 ml of stock. Use boiling stock and the soup will be plenty hot enough to serve. Alternatively, pour the soup into a saucepan and heat it through with the cream.
Blend the soup until smooth and season to taste with salt and freshly ground pepper. Add a pinch of chilli flakes if you would like the soup spicy.
Serve with ice-cold crème fraîche and crisp bread croutons.