Melt the chocolate and butter together in a small microwave-safe bowl Just heat on high for 30 second and stir or use a lower power setting (like 50%) and microwave at 30 second intervals. Let cool slightly.
Meanwhile, stir together the flour, cocoa powder, baking powder and salt. Set aside.
Combine the egg, vanilla and sugar in a bowl and mix with a fork. For puffier cookies, beat egg mixture with an electric mixer on high for 1 ½ minutes (until fluffy).
Add the melted chocolate to the egg mixture and mix just until combined. Stir in the dry ingredients and mix just until combined, then stir in the bittersweet chocolate. Let the batter stand for about 20 minutes or until it is thick enough to scoop OR chill it for an hour.
Heat the oven to 350 degrees. Line a cookie sheet with parchment paper.
Divide the dough into 6 portions and shape the portions into balls. They should be about 1 ¼ inches each. Place the balls on cookie sheet and space about 2 inches apart. Bake for 10-12 minutes (I baked mine about 13) and rotate the pan halfway.
Cool on cookie sheet for a few minutes, then transfer to a wire rack to cool completely. Note: You can stick a few chocolate wafers on the outside of the cookies while they are still hot and let them solidify as the cookies cool.