Preheat the oven to 350 degrees F. Line a cookie sheet with parchment paper.
Melt chocolate chips in the microwave (about 1.5 minutes) stirring until smooth.
Combine flour, cocoa, baking powder and salt and set aside.
In a medium bowl, cream butter with sugar and brown sugar until smooth. Beat in eggs one at a time, then stir in vanilla until well blended. Stir in melted chocolate. Mix in the dry ingredients just until everything comes together. Let stand for 10 minutes so the chocolate can set up.
Drop by rounded tablespoonfuls onto cookie sheet.
Bake for 8-10 minutes. Allow cookies to cool for a few minutes before transferring to a cooling rack.
Whisk together ingredients for the mint frosting. Once cookies have cooled for about 10 minutes, spoon about 2 tsp on top of each cookie. Let frosting set for about 5-10 minutes, then drizzle with chocolate.