Blitz the onions and carrots together in a food processor until finely chopped, or finely chop by hand. If making the croutons, heat the oven to 220C/200C fan/gas 6.

Heat the oil in a large saucepan over a medium heat and cook the chopped onion and carrot with a pinch of salt for 5-6 mins, stirring frequently until starting to soften. Stir in the garlic and peppers, and cook for 1 min more until fragrant.

Add the harissa paste, cumin seeds and chilli powder, and cook for 1 min, stirring. Add the stock and turn up the heat to medium-high, bring to the boil and cook for 15-18 mins until the veg is soft.

Meanwhile, if making the croutons, toss the bread with the oil and season well. Tip onto a baking tray and bake for 8-10 mins until deeply golden and crisp.

Transfer the veg mixture to a high-powered blender (or use a hand blender) and blend until smooth. Season and ladle into bowls. Top with the yogurt, and scatter over the croutons, if using.