1Make cake as directed on box for two 9-inch rounds; cool completely.
2Beat butter and cream cheese on medium speed until smooth and fluffy. Reduce speed to low; gradually add sugar, beating until smooth. Add vanilla, peppermint extract and food color, a drop at a time, beating until desired color is obtained.
3Split each cake horizontally to make 2 layers. Place 1 layer on serving plate; spread top with thin coat frosting. Repeat with remaining layers. Frost side and top of cake with thin coat frosting; refrigerate 10 minutes to allow frosting to firm up. Frost side and top of cake with remaining frosting. Arrange whole peppermints then sprinkle crushed peppermint around side and top of cake.
4Refrigerate until ready to serve.