Preheat oven to 350 and line muffin tins with cupcake liners.
Sift cake mix into a medium bowl. In another larger bowl mix together eggs, oil, melted butter, vanilla, buttermilk, and sour cream (or greek yogurt). Gently mix in sifted cake mix until just combined and smooth. Pour scant 1/4 cup batter into each cupcake liner. Bake 14-18 minutes until a toothpick comes out clean. Allow to cool slightly before removing from pans and allowing to cool completely.
In the bowl of a stand mixer fitted with a paddle attachment, mix butter 2-3 minutes until fluffy. Add cream cheese and mint extract and mix 1 minute more until combined. Add powdered sugar and milk and mix until fluffy and smooth. Spread or pipe onto cooled cupcakes. Top with crushed andes mints. Store in airtight container at room temperature.
(or 1/3 cup of andes mint bits - found next to the chocolate chips in the baking section at grocery stores)