In a blender, add all the ingredients except the ice cubes.
Blend at high speed until smooth. If you want a frothier blueberry smoothie, add more ice cubes, blend at high speed to combine, and serve immediately. For a sweeter smoothie, add more erythritol 1 teaspoon at a time, blend between each addition.
I don't recommend making this smoothie ahead of time, or it will form layers in the fridge. You will also lose the texture from the frozen berries and ice cubes.
For a thicker smoothie, you can add some of the ingredients below. The nutrition panel doesn't include these optional suggestions: