Place all the ingredients in a blender (except the optional). Blend on a medium speed until everything is combined. Scrape down the sides, as needed, to help the yogurt mix in. Alternatively, use an immersion blender and tall container to blend.
Serve in a large bowl or 2 smaller cups. Add granola and/or sweetener (like agave syrup) for a smoothie bowl.
Notes
Any combination of the above ingredients can be used, like switching out yogurt flavors (vanilla also works well), a different type of milk, or even different frozen berries! Agave/honey can be added in the blender, or topped at the end.
The key to making the right consistency of a smoothie is dependent on how much frozen goods are put in vs liquid vs thicker ingredients. Since ingredients can vary, I like to add less milk to start off and add a bit more as I go to get the perfect consistency.