Preheat your oven to 350 degrees and line a cookie sheet with parchment paper. I used two cookie sheets. Set aside.
If you haven’t already, chop up the chocolate bar into small chunks and divide it in half. Half will go into the cookie dough batter and half will be used to top the cookie dough balls.
In the bowl of an electric mixer fitted with the paddle attachment, cream the cubed butter and both sugars on medium high speed until smooth and creamy, about 4 minutes. With a rubber spatula, scrape down the sides of the bowl. (This step is very important because it helps hold the shape of the cookie. Under mixing will result in a flat and spread cookie.)
On medium speed, add the eggs, one at time, and beat for about 30 seconds after each addition. Scrape down the sides of the bowl after each addition. Add the vanilla and mix until combined.
With the mixer on the lowest speed, add both flours, baking powder, baking soda, corn starch, chocolate chips, half of the chopped chocolate bar, and salt. Do not over mix, that causes a dry cookie.
Using a large cookie scoop, scoop balls of the dough and then roll the top of the cookie dough ball in the other half of the chopped chocolate and place 8 balls onto the prepped pan. If you don't have a large cookie scoop, you can weigh them out to 4 ounces ball. To have a finish look, add a few chocolate chunks and chips to the top of the dough ball/
Bake for 12-14 minutes. The tops and sides will start to brown just slightly, that’s when they are done. Let them sit for 5 minutes before transferring them to a cookie rack to finish cooling.