Combine the frozen berries, plain yogurt, almond milk, ice, and stevia in a high-powered blender.
Blend on high speed until the mixture is completely smooth and creamy. You may need to scrape down the sides of the blender jug once or twice to ensure everything is incorporated.
For a soft-serve consistency, you can serve it immediately. For a firmer, scoopable texture, transfer the mixture to your ice cream maker and churn according to the manufacturer's directions.
Alternatively, pour the blended mixture into a freezer-safe container and freeze for at least 4 hours, or until firm.
Let it sit at room temperature for 5-10 minutes before scooping to soften slightly.