In a large bowl, melt butter, bittersweet chocolate and 1 cup of chocolate chips. I do this in the microwave, beginning with 30 second increments and stirring until totally melted. Set aside and let cool completely.
In a small bowl, combine flour, cocoa powder, salt and baking powder. Set aside.
In the bowl of your electric mixer, add sugar and eggs, beating on high until light and fluffy, about 2 minutes. Add in vanilla extract and melted chocolate/butter, beating for another 1-2 minutes until combined. Scrape down the sides of the bowl and the whisk or beater attachment, then remove it and stir in the dry ingredients with a large spatula until thoroughly dispersed. Fold in remaining chocolate chips. Cover with plastic wrap and place in the freezer while you make the peanut butter cookies. Let the dough sit in the freezer for at least 20 minutes.
Place peanut butter and sugar into a medium bowl, mix to combine, then add egg, mixing until well combined. Set aside.
Preheat oven to 350 degrees F. Place parchment paper (or a silpat) on an ungreased baking sheet. Remove the truffle dough from the freezer. Grease your hands with a little canola oil (cooking spray works really well, but water can also be used) then begin to scoop out about a teaspoon of dough placing them about 2 inches apart. Using your oiled (or wet hand) flatten the dough into a small round disk. Now take 1/2 - 1 teaspoon of the peanut butter dough and place it in the center of the flattened truffle dough. Scoop another teaspoon of the truffle dough and flatten into a disk. Place this over the peanut butter dough pinching the bottom layer of truffle dough together with the top. Repeat with remaining dough. Do this quickly and if you are doing the cookies in batches, refrigerate the dough in between rounds. Bake for 9-10 minutes. Let cool for at least 10 minutes on the baking sheet. Once totally cooled, if desired, you can drizzle the cookie in melted chocolate.