Preheat the oven to 210C/420F

Core Romanesco cauliflower head and break it into small florets, toss with 2 tbsp of olive oil and salt and roast in the oven for 15 minutes until cauliflower softened and looks slightly charred.

While cauliflower is being roasted, toast walnuts on a dry pan over medium heat for 2-3 minutes until fragrant.

Put a large pot of water on the stove and bring water to a boil, add 1 tsp of salt and cook spaghetti al dente according to the package directions.

In the meantime combine ⅔ of roasted cauliflower florets, walnuts, anchovies, basil and cubed parmesan cheese in a food processor and process until finely ground.

With the motor still running add olive oil through a shoot until the pesto is smooth. Stop the motor and taste the pesto sauce, add more salt, lemon juice and lemon zest and process for a few more seconds.

Drain the spaghetti and toss with the Romanesco cauliflower pesto sauce and reserved roasted Romanesco cauliflower florets.

Serve with extra Parmesan.