Position knife blade in food processor bowl; add first 4 ingredients.
Process until smooth, scraping sides of processor bowl once.
Add yogurt, and pulse 3 or 4 times or until combined.
Pour mixture into freezer can of a 2-quart hand-turned or electric freezer.
Freeze according to manufacturer's instructions.
Pack freezer with additional ice and rock salt, and let stand 1 hour before serving.
Scoop frozen yogurt into individual dessert bowls, and serve immediately.