Begin to make the frosting by draining and rinsing the cashews.
Blend the cashews with the filtered water and stevia until smooth. (Depending on your blender, you may need a little more water and you may need to scrape the sides down a couple of times.)
Refrigerate until ready to use.
Preheat oven to 325F (163C).
Combine egg whites, oil, and yogurt until smooth (with whisk or electric mixer).
Add remaining ingredients, and mix until smooth. Batter will be thick.
Bake for about 20 minutes, until firm and a toothpick comes out clean.
Let cool, then frost and enjoy!