2 thick slices of white or brown bread, roughly cut into small cubes
1/2 teaspoon ground paprika
Place the cauliflower florets in a saucepan with the stock and milk and bring to the boil. Reduce the heat and simmer for 10 minutes until the cauliflower is tender.
Meanwhile, melt the butter in a heavy-based frying pan and cook the leeks over a medium heat, stirring occasionally, for 5 minutes.
Add the mustard and nutmeg to the cauliflower, then stir in the cheese. Transfer to a food processor and whizz until smooth. Return to the pan, stir in the leeks and season with a little pepper. Heat through gently while cooking the croûtons.
Heat the oil in a large, heavy-based frying pan over a high heat. Toss the bread cubes with the paprika and cook the croûtons, stirring frequently, for 2–3 minutes until golden and crisp. Remove with a slotted spoon and drain on kitchen paper.
Ladle the soup into warmed serving bowls and scatter the croûtons over the top.