Add the frozen banana, blueberries, almond milk, Greek yogurt, and almond butter (if using) to a high-speed blender. Blend on high until the mixture becomes completely smooth and luxuriously creamy, which typically takes 60 to 120 seconds depending on your blender’s power. Once blended, taste the smoothie and adjust as needed—add a splash more milk for a thinner consistency or incorporate a touch of honey, agave, or pure maple syrup if you prefer extra sweetness. Enjoy immediately while chilled, or refrigerate for up to 24 hours for a quick, ready-to-drink option later.