I've been making copycat Orange Julius' for over 20 years now (even I don't believe it). This is the recipe that I've iterated on for a long time. It tastes super close to the original. And it's super easy to make!
Add all the ingredients to a blender cup. Blend on medium-high for 30 seconds until smooth. Enjoy!
You can store leftover sweetened condensed milk in the freezer! Just cover the can with foil and it will stay good for up to 3 months. The beauty is that condensed milk will not freeze completely solid because of the sugar content. So you can easily scoop some out whenever you need it.