Preheat your oven to 220°C/200°C fan/gas mark 7. Bring a large saucepan of water to the boil with 1/2 tsp salt for the pasta.
Grate the Cheddar cheese.
Put the blue cheese and panko breadcrumbs in a bowl and season with salt and pepper. Stir in the olive oil for the crumb (see ingredients for amount), then set your crumb aside for later.

Cut the cauliflower into florets (like small trees). Halve any larger florets and pop them into an ovenproof dish. Drizzle with oil and 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 golden brown and tender, 15-20 mins. Turn halfway through.

Meanwhile, 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.

While the pasta cooks, heat the oil for the roux (see ingredients for amount) in a saucepan on medium-high heat.
When the oil is hot, stir in the flour (see ingredients for amount). Cook until it forms a paste, 1-2 mins - you've made a roux!
Gradually stir in the water for the sauce (see ingredients for amount) and the vegetable stock paste. Bring to the boil, stir and simmer until thickened, 1-2 mins.
Stir in the creme fraiche, then remove from the heat.

Add the Cheddar cheese to the sauce and stir until melted. Taste and season with salt and pepper if needed.
Return the pan to a gentle heat and stir in the spinach a handful at a time until wilted and piping hot, 1-2 mins, then remove from the heat.
Stir the roasted cauli and the cooked pasta through the sauce. Combine well, then pour your mac and cheese back into the ovenproof dish.
Turn your grill on to high.

Sprinkle the blue cheese crumb evenly over the top, then grill the mac and cheese on the top shelf of your oven until the crumb is golden, 3-5 mins.
Serve in bowls with a drizzle of sriracha on top (careful, it's hot - add less if you don't like heat). Enjoy!