Gather your ingredients: ripe bananas, walnuts, milk (dairy or plant-based), cinnamon, honey or maple syrup, and ice cubes.
Peel the bananas and break them into chunks. Measure out about 1-2 bananas per serving, depending on the desired thickness of your smoothie.
Add the banana chunks to a blender along with a handful of walnuts. The amount of walnuts can vary based on personal preference, but around 1/4 cup per serving is a good starting point.
Pour in the desired amount of milk. Start with around 1/2 to 1 cup per serving, adjusting based on how thick or thin you like your smoothie.
Sprinkle in a generous pinch of ground cinnamon for flavor. You can adjust the amount to taste, but around 1/4 to 1/2 teaspoon per serving should suffice.
Drizzle in some honey or maple syrup for sweetness, if desired. Start with a small amount and adjust to taste.
Add a handful of ice cubes to the blender to make the smoothie cold and refreshing.
Blend everything together until smooth and creamy. If the smoothie is too thick, you can add more milk to thin it out, or if it's too thin, you can add more banana or ice cubes to thicken it up.
Once blended to your desired consistency, pour the smoothie into glasses and serve immediately. Optionally, you can garnish with a sprinkle of cinnamon or a few extra walnut pieces for added visual appeal.