Into the blender throw in:
1 cup Vanilla yogurt
3/4 cup frozen blueberries (can be fresh ones too)
11/2 cup whole milk
1 med/large banana (frozen ones are great too)
1 tbls ground cinnamon (**key)**
So simple and the kids go nutty for it. There are also variations when it comes to the fruit, but I don't stray too far from the blueberries because other berries enter tartness category too much. Strawberries, apples, grapes, sometimes raspberries, melon, have all passed the test. Oranges don't go over too well either.