Add ice cubes, frozen bananas, yogurt, peanut butter, milk, maple syrup (if using), and cinnamon to the blender.
Cover and process on medium speed for about 30 seconds, using the tamper as needed.
Increase speed to high for 15 to 30 seconds until the smoothie is thick and smooth. Adjust with more ice or sweetener (if using) to achieve the desired consistency and taste. Transfer to serving glasses.
Notes
Recipe Yield: About 2 cups (16 ounces)
Serving Size: 1 cup (8 ounces)
Make it Dairy-Free: Substitute coconut, almond, or soy yogurt for Greek. Use plant-based milk instead of dairy.