Place the cashews into a small bowl and cover with hot water straight from the kettle. Leave to one side while you carry out the next steps.
Place the butternut squash chunks and onion quarters on a baking tray. Drizzle with the olive oil and season with salt and pepper. Roast for 20 minutes.
Meanwhile, cook the pasta as per packet instructions. Then drain and reserve 1 cup of pasta water for the sauce.
Next add the garlic to the tray and roast everything for another 5 minutes.
Remove the tray from the oven and leave to cool slightly. Once cool enough to touch, peel and discard the skins off the onion and garlic and add both to a blender along with the butternut squash, stock, nutmeg and paprika. Then drain the cashews and add them to the blender and blend until smooth. Note: if the sauce is too thick, add a splash of the reserved pasta water.
Combine the sauce with the pasta then taste and season to perfection with salt and pepper.
Serve in pasta bowls with a sprinkling of chopped basil.