In a medium sized glass bowl, combine flour, baking cocoa, baking soda, baking powder and salt. Set aside.
In a large mixing bowl, cream together sugar and butter until fluffy.
Mix in eggs and vanilla.
Gradually stir the flour mix into the sugar mixture until well incorporated.
Scoop tablespoon size scoops of batter onto a parchment lined baking pan, and bake for 8-12 minutes. For a softer cookie, bake for a shorter period of time. For a crisp cookie, similar to the original “Thin Mint,” bake for 12 minutes.
Remove from pan and cool the cookies on a baking rack.
Place chocolate chips and butter in a medium sized glass bowl, and melt on high in the microwave for 2 minutes, in 30 second increments, until smooth. Stir in the peppermint oil. Dip the cooled chocolate cookies into the melted chocolate, making sure they’re completely covered, and then let set on a parchment lined cooling rack. It may take a couple of hours to completely set, depending on the temperature of your kitchen.