- In a pot of boiling salted water, cook pasta al dente. Drain.
Meanwhile, heat a little olive oil in another saucepan over medium heat. Cook the chorizo for 3 to 4 minutes. Set aside on a plate.
- In the same pan, cook the leeks for 4 to 5 minutes over low-medium heat, stirring occasionally. Set aside on a plate.
- In the same saucepan, cook the cauliflower and onion for 4 to 5 minutes, stirring occasionally.
- Add the milk mixture and bring to the boil. Simmer over low heat for 5 to 7 minutes until tender. Remove from heat.
- Using an immersion blender, emulsify the cauliflower mixture until smooth.
- Gradually add the cheese to the pan and heat over low heat, stirring, until melted.
- Add macaroni, leeks and chorizo. Season with salt and pepper and stir.
- If desired, preheat the oven to broil. Divide the mac n cheese among four cassolettes, top with panko breadcrumbs, and bake for 2 to 3 minutes, until golden brown.