Heat a pot of salted water to boiling. When ready, add spaghetti and cook until al dente (about 10 minutes).
While pasta water heats, wash and dry basil. Remove leaves from stems.
While the pasta cooks, prepare the pesto. Combine basil leaves, pine nuts (or alternative) and garlic in a food processor until finely minced. With the machine running on the slowest setting, dribble in the oil and process until smooth. Add the cheese, salt and lemon juice and process briefly, just until combined.
Once pasta is ready, drain, preserving some of the pasta water. Add pesto sauce to the pasta. Toss and add a splash of the reserved pasta water. Toss until mixed. Serve.