Preheat oven to 350 degrees. Prepare two baking sheets with parchment or silpat.
Heat chopped chocolate and butter in a microwave-safe bowl, until just melted. Whisk together the flour, baking powder, and salt and set aside.
Beat eggs, brown sugar and vanilla until the sugar has completely dissolved (about 3 minutes). Now add the melted chocolate. Mix until uniform. Add the flour mixture until just combined. Mix in the chocolate chunks.
Drop heaping tablespoons of dough 2 to 3 inches apart onto baking sheets. Sprinkle a few pieces of the chopped peppermints over each of the dough mounds, pressing lightly into the dough (The candy is prettier if you do this post-baking – lightly press the candy pieces onto the cookies hot from the oven. The heat will keep the candies in place after cooling).
Bake, rotating sheets halfway through, 10 to 12 minutes. Cool on sheets 10 minutes and then transfer to a rack to cool completely. Store cookies in an airtight container.