To toast the pine nuts, adjust the oven rack to the middle position and preheat the oven to 160 °C.

Scatter pine nuts on a baking sheet and place it in the oven to toast, shaking the pan occasionally, for 8 to 10 minutes, or until the nuts are fragrant and golden brown. Remove the pine nuts from the oven and set them aside to cool to room temperature.

Combine the pine nuts, garlic, salt and half of the olive oil in the bowl of a food processor fitted with a metal blade, or in the jar of a blender. Add half of the basil and pulse until it is finely chopped. Turn off the machine and scrape down the sides of the bowl with a rubber spatula.

Add the remaining basil, the Parmigiano-Reggiano, and the remaining olive oil and purée, stopping as soon as the ingredients form a homogenous paste and adding more olive oil if necessary to obtain a loose, spoonable pesto. 

Tip: You want to stop the machine as soon as you achieve the desired consistency, as the blade will heat the garlic and give it a bitter flavour. Also, overprocessing the pesto will incorporate too much air, making the pesto too smooth. Nancy likes to see some flecks of herbs in her pesto.

Turn the pesto out into a bowl and stir in the lemon juice. Taste for seasoning and add more salt or lemon juice if desired.

Use the pesto or transfer it to an airtight container and refrigerate for up to 2 day; any longer and it will lose its pretty green colour and vibrant flavour. Bring the pesto to room temperature, stir to recombine the ingredients, and taste again for seasoning before serving.