1In a large mixing bowl, cream the butter until it is light and fluffy.
Gradually add the granulated sugar, one cup at a time, beating well on medium speed.
Add the milk and continue to beat until the mixture is smooth and creamy.
Puree the canned mandarin oranges in a blender or food processor until smooth.
Gradually add the mandarin orange puree to the buttercream mixture, beating on low speed until well combined.
Increase the speed to medium and beat for an additional 2-3 minutes until the icing is light and fluffy.
Use immediately to frost cakes, cupcakes, or other desserts, or store in an airtight container in the refrigerator for up to one week.