Method
Begin by bringing a large pot of water with about 3 tablespoons of salt to a boil and through in the pasta.

In a food processor or hand blender, put a clove of garlic, two handfuls of chopped celery and parsely, a handful of chopped walnuts, a table spoon or so of lemon juice, lemon zest, 2-3 table spoons of olive oil, and chopped or grated parmesan cheese. Give it a blitz until everything is fine and well-combined.

Once the pasta is fully cooked, drain the excess pasta water while preserving a cup of it. Depending on how much pasta, add the pesto such that you can clearly see a visibly bright green colour. Stir the pesto through vigorously, adding pasta water and about 2 tablespoons of butter to enable a creamy texture. Taste and adjust the salt accordingly. Turn off the heat and let the pasta rest for 3 minutes or so. Ideally, you’d add enough pasta water to enable a slightly runny consistency that will clump up with time as the pasta rests with the heat off.

Ladle the pasta onto the plate, garnishing with extra grated parmesan, lemon zest, freshly cracked black pepper, and a drizzle of olive oil.