Preheat the oven to 180 degrees C.
Bring a large pot of water to the boil. Add the macaroni and cook according to packet instructions. Add the cauliflower florets for the last two minutes of the cooking time. Drain and set aside.
Put the pancetta in a frying pan over a medium heat. Cook for 4-5 minutes, until the fat has started to be released. Add the sausage meat. Break it up with your wooden spoon and cook for 8-10 minutes until golden.
Peel and chop the onion. Chop 6 of the sage leaves. Add the onion and sage to the frying pan - cook, stirring, for 2 more minutes. Remove from the heat.
To make the sauce, melt the butter in a saucepan over a medium heat. Whisk in the flour. Turn off the heat, then gradually add the milk, whisking all the time. Turn the heat back on and bring the sauce to a gently simmer, still whisking, until the sauce thickens. Stir in 200g of the cheese.
Get a large ovenproof dish. Put the macaroni and cauliflower, sausage meat mix and cheese sauce in the dish. Mix until evenly combined. Top with the remaining cheese, breadcrumbs and sage leaves. Bake in the oven for 25-30 minutes until bubbling and golden.