Add the frozen cranberries, banana, protein powder, plant-based milk, maple syrup or agave (if using), and vanilla extract to a high-speed blender.
Blend on high for 1 to 2 minutes, or until completely smooth.
Taste and adjust sweetness if needed.
Pour into glasses and serve immediately.
Notes
Use very ripe banana: Cranberries are naturally very tart, so the natural sweetness of overripe bananas is great to balance the flavor without needing lots of added sugar.
To adjust the consistency: Use fresh vs. frozen fruit and adjust the amount of liquid. Frozen fruit helps make a thick, creamy consistency.
For the smoothest smoothie: Use a high-speed blender (great when using frozen ingredients!) and add the liquids/softest ingredients closest to the blades. Pause the machine if needed to scrape down the sides.