1. Whisk together all the sauce ingredients, except 1 tbsp of the grated cheese, and season with ground black pepper.
2. Cook the spinach, with no extra water, in a medium saucepan until just wilted. Remove, squeeze out all the excess liquid and chop. Spoon over the base of a shallow, heatproof dish.
3. In the same saucepan, cook the macaroni in boiling water for 7–10 minutes until tender. Add the chopped leek for the last 2–3 minutes of cooking time.
4. Drain the macaroni well and stir in the sauce ingredients. Spoon on top of the spinach and sprinkle with the reserved cheese and breadcrumbs.
5. Pop under a hot grill for 2–3 minutes until well browned. Serve immediately.
- “You can use frozen spinach. Measure out about 85g (3oz) and squeeze well to remove all excess liquid before using.”