Preheat oven to 350°. If pine nut s are not already toasted, toast them on a baking sheet lined with parchment paper until golden brown. With a spatula, toss the pine nuts halfway through. The toasting process should take about 5–7 minutes. Be careful not to overcook them. Transfer to a food processor and let cool.
Add parmesan, lemon zest, lemon juice and garlic and pulse until finely ground, about 1 minute. Add basil and place the top back on. With the motor running, add oil in a slow and steady stream until pesto is mostly smooth, with just a few flecks of green, about 1 minute. Season with salt to taste.
To store, put in an airtight container and top with a layer of olive oil to seal and prevent browning. Store in the fridge for up to 2 days.