Toast walnuts in a dry pan for 3–4 min over medium heat until fragrant. Cool slightly.

Blend walnuts, Parmesan, garlic, basil, lemon zest, lemon juice, and olive oil until textured but fairly smooth. Add cold water to loosen. Season with salt and black pepper.

Cook pasta in salted water as per packet instructions.

Add peas for the last 3 min of cooking. Reserve about 100ml pasta water before draining.

Blend cottage cheese with two-thirds of the walnut pesto and a splash of pasta water for a creamy sauce.

Drain pasta and peas, return to pan. Add spinach and stir over low heat for 1–2 min until wilted.

Remove from heat, stir in cottage-cheese pesto mixture and remaining Parmesan.

Add enough pasta water to make the sauce silky and glossy.

Divide into two bowls, spoon remaining walnut pesto on top.

Finish with black pepper, a squeeze of lemon, and extra toasted walnuts if desired.