In a dry pan, lightly toast the pine nuts over a medium-low heat until aromatic and a you notice a slight colour change. Keep a watchful eye on the pan, so they don't burn or get too golden! Remove from heat and let cool.
Prep the other ingredients while the pine nuts cool. Wash and thoroughly (but carefully) dry the basil leaves - make sure to remove as much excess moisture as possible (a salad spinner is good for this). The leaves cannot be wet. Zest and juice lemon. Peel garlic.
Place the basil, nuts, cheese, garlic, lemon zest, juice (start with 1 Tbsp) and a pinch of salt and pepper into a small food processer or a blender.
Pulse a few times until roughly chopped and combined. You may need to scrap the side down with a spatula a few times.
With the food processor running, gradually pour in the olive oil through the hole in the lid. I find it easiest to put the oil measure into a milk jug with a spout and pour it in from there.
Turn off the food processor. Taste test and adjust seasoning. Do you think it needs more salt or pepper? The remaining lemon juice? More garlic? Do you want it thin by adding more olive oil? Make it yours.