Add the ingredients to your food processor. Process until completely smooth, stopping once to scrape the sides and bottom of the bowl.
Using a spatula, transfer the mixture to a square 9-inch pan. Cover with cling wrap, and freeze for 1 hour.
Remove the pan from the freezer. Use a fork to stir the already-frozen edges into the still-soft center. If the edges are very frozen, you might need to scrape them with a knife. Stir the mixture until smooth, then spread it evenly in the pan.
Cover again, and place in the freezer for 3 more hours, repeating the process of stirring the yogurt every 60 minutes.
When the entire mixture is frozen, serve immediately as soft-serve yogurt (use chilled bowls), or freeze for two 2 more hours for a firmer consistency that you can scoop out with an ice cream scoop.
If frozen overnight, remove the yogurt from the freezer 10 minutes before serving to allow it to soften.
Nutrition info assumes that a sugar-free sweetener was used. You can use any granulated sweetener instead of stevia, though a powdered sweetener is best.