I just made this now and it's delicious!
You can eyeball the amounts really
1 Cup of Frozen Berries
Enough orange juice to cover frozen berries
5 table spoons of Kefir, or plain yogurt
Place in the berries and orange juice in to the blender and blend until smooth. You can add ice if you want. Place the Kefir or Yogurt in and place it on a 'stir' mode, just slowly blend it in.