1. Preheat oven to 325°. Line a baking sheet with parchment paper and set aside.
2. In the bowl of your stand mixer, combine half melted butter and brown sugar until smooth.
3. In a separate bowl, whisk together pudding mix, flour, corn starch, cocoa and baking powder, set aside.
4. Add in the egg, yolk and vanilla and mix until smooth.
5. Pour in the dry ingredients slowly and mix until just combined.
6. Fold in the chocolate chips until evenly distributed.
7. Chill your dough for at least 30 minutes in the refrigerator. Dough may be very hard, but this will ensure that they will be nice and thick. Once you start working it with your fingers, it will soften up.
8. Roll dough into small balls, about 1 - 11/2 tbs each, and flatten with fingers on baking sheet. The way you shape your balls is pretty much how they will stay because they mostly keep their shape.
9. Cut up a peppermint pattie. I cut mine down the middle, across, and diagonal both ways making 6 little triangles. Press one triangle on top and the rest on the sides. No need to be neat, just place them anywhere on the sides.
10. Repeat the last step for all of your cookies, then place in preheated oven and bake for 10 minutes.
11. When done, they may appear to be a bit under done, but they will firm up as they cool and be super fudgy. If there is some peppermint pattie that has melted off onto your baking sheet, just break it off, it will come right off.
12. Let them cool on baking sheet for about 10 minutes then move to wire rack or counter to finish cooling.