Place the basil leaves in a blender or food
processor with the garlic and salt and run the
machine until they form a puree, or pound in a
pestle and mortar.
Add the nuts and measured cheese
and blend until smooth, scraping the mixture from
the sides as necessary, or pound in the mortar.
Gradually add the oil a drop at a time until the
mixture becomes a thick green sauce. Add a good
grinding of pepper.
Meanwhile, cook the spaghetti
according to the packet directions. Drain and return
to the saucepan.
Add the pesto and toss over a
gentle heat until glistening. Serve dotted with the
butter and Parmesan cheese.