Make the ragu first - heat the oil in a flameproof casserole over a high heat. Season the lamb and add it to the casserole. Cook for 6 to 8 minutes, turning until browned all over. Then add the passata, 3 of the rosemary sprigs, fennel seeds, garlic, anchovies and chopped chilli. Season with salt and pepper, reduce heat to a simmer, cover and cook for 2 hours or until lamb is tender.
Once lamb is cooked, turn off the heat and set aside.
Preheat the oven to 200C/180C fan/gas 6.
Cook the macaroni according to the instructions on the packet, drain and set aside.
Meanwhile, make the sauce for the macaroni - melt the butter in a saucepan over a medium heat. Add flour and cook, stirring, for 1 minute, then gradually add the milk and bring to a simmer. Cook for 5 minutes or until thickened. Stir in the macaroni and 50g of the pecorino. Season with salt and freshly ground pepper, to taste.
Top the ragu in the casserole with the macaroni and cheese (starting in the centre and working your way out to the edges), then scatter over the feta, panko breadcrumbs, the leaves from the remaining rosemary sprig and the remaining 50g of pecorino.
Bake in the oven for 20 minutes or until golden and bubbling. Leave to stand for 5 to 10 minutes before serving.
Enjoy with some authentic focaccia…and look forward to the leftovers, if there are any!!