With an electric mixer, cream the butter with the sugar until the mixture is light and fluffy. Add in mint extract and cocoa powder.
Add flour, baking powder and salt. Mix until it forms a dough.Divide the dough in half. On a sheet of wax paper, form each half into an 8-inch long log. Chill the logs, wrapped in the wax paper, for at least 2 hours or overnight. (If you’re pressed for time, 30 minutes in the freezer works well too!)
Heat the oven to 300°F. Line baking sheets with parchment paper.
Cut the logs into ¼-inch-thick slices with a sharp knife. Arrange the slices 2 inches apart on baking sheets. Bake the cookies on the top rack of the oven for 22-26 minutes.Transfer to wire racks to cool.
Heat melting chocolate chip in microwave for 2 minute. Let sit 3-4 minutes. Stir gently and continue heating in 15 second increments until smooth.*Dip each cookie fully into the chocolate, tapping off excess. Transfer to a parchment lined tray. Let cool to set. Store cookies in an airtight container.
Dipping chocolate just works best. You can purchase Ghirardelli Melting Wafers at most grocery stores. I buy my melting chocolate in bulk on Amazon. If you really want to use chocolate chips instead, I suggest melting 1/2 a tablespoon of shortening or 2 tsp coconut oil in with the chocolate chips, to thin it out and make it easier to dip the cookies.Recipe yields 65 cookies. You can bake 20-24 cookies on each tray, so they're all baked in 3 batches.