Preheat the oven to 180°C (fan)/200°C/gas mark 6.
Tip the tomatoes, carrots, red onions and garlic into a roasting tray. Toss with the oil and season with salt and pepper. Roast for 45 minutes until soft and golden.
While they're roasting, whip up the croutons. Tear the bread into rough bite-sized pieces, spread them out onto a baking tray and mix thoroughly with the pesto and oil and a generous pinch of salt.
Put them in the oven, on the shelf above the veg, and cook for 8-10 minutes, stirring once, until crisp and toasty (timings may vary depending on what type of bread you use). Remove from the oven and set aside.
When the vegetables are soft and golden, scrape them all into a large saucepan along with any lovely caramelised sticky bits from the bottom of the roasting tray.
Add the hot stock and heat gently over a medium heat. Simmer for 15 minutes then, using a stick blender, purée the soup, adding a little extra stock if needed until you get the consistency you like.
Stir through the tomato pesto and season to taste with salt, pepper, and a pinch of sugar.
Stir well then serve with a handful of crunchy pesto croutons and a few basil leaves.