Add all of the ingredients to a blender (or blending container, if using an immersion blender). Blend on high speed until very smooth and serve immediately.
Strawberry banana smoothies don't store well, so it should be served right after blending. If you don't have frozen strawberries, the bananas can be frozen instead, for a creamier smoothie.
Notes
This makes enough for a generous serving for two people, or about a glass each for three people.