Place all the ingredients into a high powered blender in the order listed.
Secure the lid and blend, starting on low and working up to high speed. If the smoothie is too thick, use the tamper to keep it moving in the blender. I blend until the smoothie is smooth with most of the blackberry seeds intact. This is just a preference thing, you can blend until it’s completely smooth if you’d like.
Pour into containers and and drink within the day. It will keep refrigerated until the next day, but it’s not quite as good!