1. In a large mixing bowl, add sugar, and butter. Beat until creamy.
2. Throw vanilla and mix well.
3. In a separate bowl, combine flour, cocoa powder, baking powder, and salt. Whisk well.
4. Add butter mixture in 2 additions, into the bowl with flour. Mix to incorporate.
5. Throw chocolate and mix to make crumbly dough.
6. Roll dough into a log, and warp it with saran wrap. Put dough in refrigerator for 1-2 hours to chill.
7. Then, slice dough into ½-inch thick round, and place it on baking sheet, about 1-inch apart.
8. Preheat oven to 325 degree F or 160 degree C.
9. Place baking sheet in oven, and bake for about 12 minutes or until the edges are dry but the center is still a bit moist.
10. Remove from oven and let the cookies cool in pan for 5 minutes.
11. Transfer it to wire rack and let it cool completely.
12. Serve cookies with a cup of hot milk.
Store cookies in an airtight container for up to a week or freeze for a month.