Place frozen strawberries, bananas and blueberries into a blender.
Pulse to chop into small pieces, you almost want it shredded. Make sure you pulse and not blend so that it doesn't get stuck.
Add the milk and nut butter if using.
Blend or pulse on low while stopping to move the mixture around. If you have a vitamix, the tamper will work well for this. Do not blend on high or the heat will melt the mixture.
Once it is the consistency of a thick frozen yogurt, pour into a bowl and serve topped with the toppings you want!
Notes
This works best using only frozen fruit. You can freeze fresh fruit to use at a later date.
By blending the frozen fruit first, you are getting it into small pieces so that it blends smoother and faster.