Beat the egg white until it forms stiff peaks. Quickly beat into the nectarine puree. Transfer to a stainless steel bowl or ice trays without the dividers, cover, and place in the freezer. Every 2 to 3 hours, break up the granita with a fork or a food processor and return to the freezer It should not be frozen solid when you serve it, but should break apart easily.
NOTES : A granita is a fruit ice, made here by just pureeing the fruit with a very small amount of sweetening, folding in an egg white, and freezing until not quite solid. You break up the granita a few times with a fork or in a food processor during the freezing process so that it won't have too many ice crystals.
I probably wouldn't use a raw egg white in the Granita due to the risk of contamination. I would try pasteurized egg whites.