Preheat your oven to 220°C/200°C fan/gas mark 7. Bring a large saucepan of water to the boil with ½ tsp salt for the macaroni. 

Meanwhile, trim the Brussels sprouts. Halve them through the root, then pop them onto a baking tray. 

Drizzle with oil, season with salt and pepper, then toss to coat. Spread out in a single layer.

When the oven is hot, roast on the top shelf until browned and tender, 15-18 mins. Turn halfway through.

When your pan of water is boiling, add the macaroni and bring back to the boil. Cook until tender, 12 mins.

Once cooked, drain in a colander and pop back into the pan. Drizzle with oil and stir through to stop it sticking together.

Meanwhile, halve, peel and thinly slice the onion. Trim the root and dark green leafy part from the leek and discard. Halve lengthways, then thinly slice.

Heat a drizzle of oil in another large saucepan on medium-high heat. 

Once hot, add the onion and leek. Season with salt and pepper and fry, stirring occasionally, until golden, 8-10 mins.

While the veg cooks, grate the Cheddar cheese. Peel and grate the garlic (or use a garlic press). 

In a small bowl, combine the breadcrumbs, hard Italian style cheese and olive oil for the crumb (see pantry for amount).

Season with salt and pepper, then set your cheesy crumb aside.

Once the onion and leek is cooked, add the garlic and stir-fry for 1 min more. 

Melt in the butter (see pantry for amount), then stir in the flour (see pantry for amount). Cook until it forms a paste, 1-2 mins - you've made a roux! 

Stir in the water for the sauce (see pantry for amount) a little at a time, followed by the veg stock paste. Bring to the boil, then stir and simmer until thickened, 1-2 mins.

Stir the creme fraiche and Dijon mustard into the sauce, then remove from the heat. Stir through the Cheddar until melted, then season with salt and pepper.

Meanwhile, turn your grill on to high.

Once the Brussels sprouts and macaroni are cooked, gently stir them through the cheese sauce. Add a splash of water if it needs loosening a little.

Transfer the mac & cheese to an appropriately sized ovenproof dish and sprinkle over the cheesy crumb.

Once hot, grill until golden and bubbling, 3-4 mins. 

When ready, allow it to stand for a couple of mins before sharing between your bowls.