Peel and slice the banana into rough chunks. For the thickest result, use a pre-frozen banana sliced into coins and stored in a freezer bag.
Pour 1 cup (240ml) of milk into the blender first. This protects the blades and helps frozen ingredients blend more efficiently.
Spoon in the Greek yogurt, then add the vanilla extract and a pinch of cinnamon if using. Do not blend yet.
Add the frozen blueberries on top of the yogurt, then place the banana chunks on top. Do not fill the jar above the maximum fill line.
Secure the lid and blend starting on low, increasing to high speed. Blend for 45 to 60 seconds until completely smooth with no visible chunks. Use a tamper if needed to push fruit toward the blades.
Taste the smoothie and adjust as needed: add honey for sweetness, more frozen blueberries for thickness, or a splash of milk to thin it out. Blend again briefly after any additions.
Pour into two tall glasses or mason jars, garnish with fresh blueberries, a banana slice, and a dusting of cinnamon if desired. Serve right away for best texture.