Preheat the oven to 350ºF (180ºC). Line a baking sheet with parchment paper and spread the pine nuts out into an even layer. Place the pine nuts in the preheated oven and toast them until they are light gold and fragrant, about 7 to 9 minutes. Shake the pan halfway through toasting. Set aside to cool.
Tear the basil leaves and stems and place them inside a large tall jar, food processor, or blender. (if using a jar and a handheld immersion blender you may need to do this in a few batches as the basil may not fit all at once). Pulse the basil a few times to start breaking down the leaves.
Add the toasted pine nuts, grated Parmesan cheese, garlic clove, and ¼ teaspoon of flaky salt to the jar. Process everything together until the mixture is coarse and chunky.
Add the olive oil and blend the pesto for 5 to 10 seconds more. Taste and adjust the seasoning and/or add more salt to your liking. Spoon the pesto into a small clean jar and store it in the fridge, sealed with an airtight lid, for up to one week.
Notes
When choosing fresh basil, avoid any wilted or discolored leaves. Rinse and pat dry the leaves before using.
Avoid pre-grated Parmesan cheese, as it can clump.
Once the pesto is made, taste it and adjust the salt as needed. The Parmesan cheese adds saltiness; however, you may need to add a little bit more to suit your taste.
Storage
Pesto will keep in an airtight container in the refrigerator for up to five days. It also freezes well for longer storage.