Add 2 tablespoons olive oil, the anchovy, garlic and walnuts to a pan over a medium heat. Cook until the anchovies have melted, and the walnuts have browned. Add the tomato paste and stir. Cook for 2 minutes, until it turns a deep red. Remove the pan from the heat and add to a food processor (or mortar and pestle). Add the dried chilli, then blitz. Pour in the remaining ¼ cup of olive oil and blitz again. Stir in lemon zest and finish with the Parmigiano Reggiano.

 When ready to eat, toss the pesto with hot al dente pasta in a pan, along with a good splash of pasta cooking water (start with ¼ cup and work up from there) and a squeeze of lemon juice to taste. Forcefully stir it to bring it all together, adding more cooking water if you need. Serve with a extra shaved Parmigiano Reggiano.