Peel the garlic, then pound in a pestle and mortar with a pinch of sea salt.
Pick, roughly chop and add the basil leaves, then bash to a paste (or pulse in a food processor).
Add the pine nuts (very lightly toast first, if you like) to the mixture and pound again, then stir in half the Parmesan.
Drizzle in some oil – you need just enough to bind the sauce and get it to an oozy consistency.
Add most of the remaining cheese, then season to perfection with salt and black pepper. Have a taste, and keep adding a bit more cheese or oil until you are happy with the taste and consistency.
Add a squeeze of lemon juice at the end to give it a little twang, if you like, but it’s not essential.
You may think it’s nice to toast the pine nuts until they’re golden, to give them a nutty taste, but the really good pestos I’ve tasted in Italy just have them very lightly toasted, to give a creaminess rather than a nuttiness.