With a hand-held mixer, beat the egg whites in a medium bowl, until frothy. While still beating, slowly add the sugar and beat on high speed until the egg whites are stiff and shiny, about 4 minutes. (This can also be done in the bowl of an electric mixer fitted with the whisk attachment).
In another bowl, whisk the yogurt until smooth. Fold in the egg whites. Transfer the mixture to an ice cream freezer and freeze according to the manufacturer's instructions. Freeze in a quart container until ready to serve.
* Raw Egg Warning
Food Network Kitchens suggest caution in consuming raw and lightly cooked eggs due to the slight risk of salmonella or other food-borne illness. To reduce this risk, we recommend you use only fresh, properly refrigerated, clean grade A or AA eggs with intact shells, and avoid contact between the yolks or whites and the shell. For recipes that call for eggs that are raw or undercooked when the dish is served, use shell eggs that have been treated to destroy salmonella, by pasteurization or another approved method.