Add the basil leaves, pine nuts, Parmesan cheese, and garlic to a food processor or blender. Pulse until the mixture is finely chopped. With the machine running, slowly drizzle in the olive oil until the pesto reaches your desired consistency.

Season with salt and pepper to taste, and blend briefly to combine. If desired, add the lemon juice for a hint of acidity.

Store in an airtight container and refrigerate for up to a week or freeze for later use.