First, ensure that your applesauce is smooth. If yours isn't, then briefly puree it with an immersion blender (hand held stick blender).
Also, ensure the applesauce and butter are at room temperature.
Add the butter, apple sauce and vanilla to a mixing bowl, and beat with an electric mixer until smooth.
Sift in the powdered confectioner's sugar a little at a time, beating until thick, smooth, and creamy.
TIP: If necessary, add a little more powdered sugar to thicken, or a tablespoon of milk to thin.
Store it covered in the refrigerator until you're ready to use it.
