Place the pine nuts on a baking sheet and lightly toast in the oven for 3 to 5 minutes. Set aside to cool completely.
In the container of a food processor, combine the basil with half the Parmesan, the garlic, pine nuts and salt. Process without the feed tube in place.
Gradually pour in the olive oil and continue to process until even. Verify the seasoning.
Cook the spaghetti al dente (1 minute less than the time indicated on the package).
Keep one or two ladlefuls of cooking water from the pasta to dilute the pesto if needed.
Drain the pasta.
In a large bowl, place the hot pasta and add the pesto. Stir well.
If needed, add a bit of cooking water.
Garnish with Parmesan and serve.
Tip:
Pesto may also be prepared in a mortar. Crush together the basil, garlic, Parmesan, pine nuts and salt until the mixture is even. Pour the oil into the mortar and stir well.