Bring a large pan of salted water to the boil and cook the spaghetti until al dente.

Meanwhile, toast the walnuts in a dry frying pan over a medium heat for 4-5 minutes, stirring often, until golden, then tip them into a blender.

In the same pan, add the olive oil, garlic and chilli and cook briefly, just until fragrant.

Add the cavolo nero and cook for a few minutes, until wilted, then transfer everything to the blender.

Drain the pasta, reserving a mug of the cooking water.

Add about 150ml of the pasta water to the blender with a pinch of salt and pepper, then blitz until smooth.

Toss the sauce through the pasta, loosening with a little more pasta water if needed.

Stir through the lemon juice and adjust the seasoning to taste.

Divide between bowls and finish with a handful of rocket, a drizzle of olive oil and plenty of black pepper.