Combine basil, garlic, pine nuts, and lemon juice (if using) in food processor. Pulse until finely chopped.
With the food processor running, slowly add the olive oil in a steady stream. Let process, scraping down the sides of the food processor bowl as needed, until mixture is smooth.
Add the parmesan cheese and pulse until just combined.
Add the cream to the mixture and pulse until just combined. Season with salt and pepper.