If you're using pestle and mortar, start by crushing the garlic, then add the basil and grind until the leaves are completely crushed. Add the pine nuts and cheese and then continue grinding while adding the olive oil little by little until you get the right consistency.
If you're using a food processor, add all the ingredients together and give it a couple of pulses, then start adding the oil little by little in a thin stream and keep blending until it becomes creamy and lighter in color.
Adjust with salt and add more cheese or pine nuts to your taste.
NOTE: You shouldn't blend more than a couple of minutes, otherwise the pesto will heat up and the basil leaves will oxidize.
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Notes
Fridge: Store in an airtight container with a thin layer of olive oil on top to prevent oxidation. Keeps for 3–4 days.Freezer: Freeze in small portions (like in an ice cube tray) and transfer to a freezer-safe bag or container. Keeps for up to 3 months. Thaw in the fridge or stir into hot pasta to reheat gently.Avoid heating pesto directly on the stove—this can cause the basil to lose flavor and the cheese to separate.