Cook the pasta according to the packet instructions, then drain, rinse and set aside.

Melt the butter and garlic purée in a large flameproof pan over a medium heat.

Reduce the heat and add the flour.

Whisk until it forms a smooth paste.

Start adding the milk, whisking in a little at a time until fully combined.

Increase the heat and bring the sauce to a gentle simmer, whisking often.

Once simmering, keep whisking for about 3 minutes until the sauce has thickened.

Take the pan off the heat.

Preheat the oven to 180°C (fan) and get an ovenproof dish ready.

Whisk in the salt, pepper and mustard, then stir through the sliced cooked Brussels sprouts.

Add the pasta and most of the cheese.

Stir gently until the cheese has melted and everything is coated in the sauce.

Tip the mixture into the ovenproof dish and spread it out evenly.

Sprinkle over the remaining cheese.

Bake for 20–25 minutes, until the top is golden and bubbling.