Combine the butter, sugar, and vanilla in a bowl and stir together until smooth. Stir in the muesli mix until well combined. Scoop into 1 - 1 1/2 inch balls and roll between your hands to smooth them. Place in an airtight container and refrigerate at least 8 hours before serving. Enjoy!
Notes
This recipe can be made using an electric mixer as well. Personally, I find it easiest to use a bowl and a wooden spoon most of the time.