To your finished milk kefir, add strawberries, vanilla extract, and liquid stevia.
Use an electric hand mixer to blend it all together right in the jar. (saves on dishes!) :)
Next, place your flavored kefir on the countertop covered with a plastic lid for 2-4 hours and have it go through a second ferment.
You can enjoy immediately or refrigerate covered for up to 2 weeks. The longer it stays in the refrigerator, the more sour it will get.