Put a pan of salted water on to boil, when the water is boiling add the macaroni and cook for around 10-20 minutes until it is al dente. Preheat the oven to 200C.
In a saucepan melt the butter, then add the flour and cook out for a couple of minutes whilst stirring continuously. Add half the milk stirring all the time until the mixture thickens, stir vigorously to smooth out the mixture before adding the other half of the milk, stirring until the mixture has thickened again.
In a frying pan, add the bacon lardons and cook until the fat has rendered and they have become crispy and golden. Add the lardons, 150g of the grated cheese and the Smoked Chilli Harissa to the cheese sauce and season to taste.
Drain the pasta, mix with the cheese sauce and put in a heavy baking dish. Sprinkle on the rest of the grated cheese and the breadcrumbs and put in the oven for 40 minutes or until the top is golden and crispy.