I put a cup of frozen blueberries in my food processor (I have a Ninja, love it) and let it sit for about 45 minutes to thaw slightly. Then I added 1/4 cup of vanilla yogurt and a tablespoon of peanut butter and blended it up.
I do this, too - it is awesome! I add some Torani syrup and xanthan gum and freeze for a short bit before processing. I hear bananas work well - but I like my blueberries!! For variety, I switch out the syrup and yogurt flavors....