Select a ripe Hass avocado that gives slightly when pressed, then slice it lengthwise, twist apart, and remove the pit. Scoop all the flesh out with a large spoon, cutting away any brown spots.
Use a frozen banana for the best results: slice into 1-inch (2.5cm) rounds and freeze for at least 2 hours or overnight. If using a fresh banana, keep the full cup of ice to compensate for the chill.
Measure out 1 cup (240ml) milk, 2 tablespoons (42g) honey or maple syrup, 1 teaspoon (5ml) vanilla extract, a pinch of salt, and 1 cup (240ml) ice cubes. If using optional add-ins such as Greek yogurt, chia seeds, or hemp seeds, measure those out now as well.
Pour the milk into the blender first, then add the avocado flesh, frozen banana, honey, vanilla extract, salt, and any optional add-ins. Add the ice last, on top of everything else.
Blend on low for 10 seconds, then increase to high and blend for 45 to 60 seconds until completely smooth with no chunks. Scrape down the sides with a rubber spatula if needed, then blend for another 10 to 15 seconds.
Taste the smoothie and add more honey if needed or a splash of milk if it is too thick, then blend briefly again. Pour into tall glasses and serve immediately for the best color, flavor, and texture.