Heat the oven to 160C/fan 140C/gas 3. Start with the ragu - toss the beef in the salt, pepper and flour and shake off the excess. Heat 1 tbsp of the oil over a medium high heat in a large shallow casserole. Brown the beef chunks in 2 batches, until they have a good colour on all sides (approx. 4 minutes for each batch), then scoop them out and do the next batch, adding the remaining 0.5 tbsp of oil.
Once all the beef has browned, tip it back into the casserole and add the onion, carrot, and star anise. Cook for about 5 minutes, stirring occasionally, then stir in the tomato purée. Add the stock, wine, and passata and bring to a simmer. Cover the pan with foil and put on a lid to create a seal. Transfer to the oven and cook for 3 hours, then check the beef is done – you want it to fall apart easily. If it doesn’t, put it back in the oven for another 30 minutes to an hour. Stir in the basil and check the seasoning, adding more if needed.
After 2.5 hours of the beef being in the oven, make the mac ‘n’ cheese - melt the butter in a medium saucepan over a medium low heat, then stir in the flour. Keep cooking and stirring for 3 minutes, then gradually whisk in the milk until you have a smooth sauce.
Increase the heat to medium and add the mustard powder, cheddar, gruyère and emmental, and stir until melted. Season, to taste, if required with salt and freshly ground black pepper.
Turn up the oven to 220C/fan 200C/gas 7. Cook the macaroni until just al dente (approx. 7 to 8 minutes), drain in a colander then rinse under cold water and drain well. Mix with the cheese sauce.
Top the ragu with the mac ‘n’ cheese. Bake for 20 to 30 minutes until golden and bubbling. Rest for 5 minutes before serving.