Pour the whole milk into the blender first: Add the Greek yogurt, maple syrup, and vanilla extract. Starting with the liquid ingredients helps the blender circulate the thicker ingredients more easily.
Add the pumpkin puree and frozen banana: Break apart any banana slices that have frozen together in a solid clump before placing them in the blender.
Add the pumpkin pie spice, cinnamon, and fine salt. The salt should be only a small pinch; it is there to sharpen the pumpkin and spice flavors rather than make the smoothie taste salty.
Add the ice cubes last: If your blender is less powerful, start with half of the ice and add the rest after the first blend.
Blend on high for 45–60 seconds: Stop and scrape down the sides if necessary, then continue blending until the smoothie is completely smooth and creamy. There should be no visible ice pieces or streaks of pumpkin.
Check the texture: If the smoothie is too thick, add milk 1–2 tablespoons (15–30 mL) at a time and blend briefly. If it is too thin, add a few more ice cubes or a small amount of additional frozen banana and blend again.
Divide the smoothie between two glasses: Top with optional whipped cream and a light dusting of cinnamon if desired. Serve immediately for the thickest texture.