Green mac and cheese with bacon crumb

Method

1. Strip the cavolo nero leaves from their stems and roughly chop. Finely slice the stems and put in a small pan with the vinegar, water and sugar. Bring to the boil, then leave to cool.
2. Meanwhile, heat the grill to high, then cook the bacon until completely crisp. Drain on kitchen paper then, once cool enough to handle, finely chop. Stir through the breadcrumbs with lots of black pepper.
3. Fill a small saucepan with boiling water from the kettle, add the chopped cavolo nero leaves and cook over a high heat for 3-4 minutes. Drain and set aside.
4. Melt the butter in a saucepan over a medium heat, add the flour and cook for 1 minute, then slowly whisk in the milk until you have a smooth sauce. Fold in both cheeses, keeping a large handful aside for the topping. Stir until melted and completely combined, then stir in the mustard. Transfer to a blender with the cavolo nero leaves (give them a squeeze as you do so to remove any excess water) and whizz to a smooth, deep green sauce. Taste and season with salt and a splash of the stems’ pickling liquid.
5. Heat the oven to 170°C fan/gas 5 and bring a pan of salted water to the boil. Cook the macaroni in the water for 6-8 minutes (you want it to be al dente, as it will continue to cook in the oven).
6. Drain the pasta and stir in the green sauce, then strain the pickled stems and add two thirds of them to the pasta and sauce. Transfer to an ovenproof dish and sprinkle with the bacon crumb, the remaining pickled stems and reserved cheese. Bake for 15-20 minutes until golden and bubbling.