In a mixing bowl, cream together the butter, granulated sugar, and brown sugar until smooth. Beat in the egg.
In another bowl, whisk together the flour, baking powder, salt, cocoa powder, and peppermint extract. Gradually mix this into the butter mixture.
Drop rounded tablespoons of dough onto a baking sheet and flatten slightly.
Bake for 10 minutes, then let cool.
For the chocolate coating, melt the baking chocolate with vegetable oil and peppermint extract. Dip each cookie in the chocolate and let them set on parchment paper.
Notes
Store cookies in an airtight container for freshness. You can also adjust the peppermint extract to your taste.
Keyword chocolate cookies, peppermint cookies, Thin Mint Cookies