Cook the macaroni according to the packet instructions until al dente. Drain and set aside.
Meanwhile, prepare the vegetables. Finely slice the green onions and celery, then chop the asparagus and tenderstem broccoli into roughly 1–2cm pieces, discarding any woody ends.
Preheat the oven to 180°C. Heat 1 tablespoon of the olive oil in a large pan over a medium heat. If you have an ovenproof pan, this makes things even easier.
Add the green onions and cook for about 1 minute, then add the celery and cook for another minute until beginning to soften.
Add the asparagus and broccoli and cook, stirring often, for around 5 minutes.
Add the spinach along with 200ml water and cook until the spinach has wilted down completely.
Remove the pan from the heat and use a stick blender to blend the vegetables into a smooth-ish sauce. It doesn’t need to be perfectly silky.
Stir in the double cream, half of the parmesan and the basil. Taste and season if needed.
Add the cooked macaroni and stir really well so the pasta is evenly coated in the green sauce.
Sprinkle over the breadcrumbs and the remaining parmesan, then drizzle over the rest of the olive oil.
Bake for about 15 minutes, until the top is golden and the pasta is bubbling around the edges.
Serve hot.