If you don’t have an ice cream maker – you can pour the frozen yogurt mixture into a ziptop bag, squeeze out all air, and seal. Freeze, lying flat, until solid. Remove from freezer and break into chunks small enough to fit into the bowl of your food processor or a high-powered blender. Pulse until completely smooth. If adding mix-ins, either fold them in or pulse until desired consistency is reached, then pour into an airtight container. Cover and freeze until ready to serve.