Line a mini muffin pan with 12 tin foil cupcake wrappers and set aside
Place chocolate and butter in a medium microwave safe bowl; melt by microwaving the chocolate and butter in 30-second increments and stirring in-between
Use a teaspoon to coat the bottom of each cup with melted chocolate; place muffin pan in fridge
Combine buttercream with Oreo crumbs in an electric mixer with paddle attachment or with a spoon
Remove pan from fridge and pipe buttercream into center of each cup (about 1 tablespoon)
Spoon melted chocolate over buttercream and around edges so that coated on all sides
Chill for one hour in refrigerator before serving; store in refrigerator up to one week
Recipe by Keep It Sweet Desserts at http://www.keepitsweetdesserts.com/mint-cookies-and-cream-buttercream-cups/