In a medium bowl whisk together the flour, cocoa powder, baking powder, baking soda and salt. Sift the cocoa powder first if it's lumpy.
In a separate bowl beat together the butter, brown sugar and granulated sugar until smooth.
Mix in the melted dark chocolate. Ensure the chocolate is cooled first. To melt the dark chocolate, finely chop first. Then melt in the microwave or a double boiler. If using the microwave, use 45-second intervals on medium power and stir between each interval. If using a double boiler, be sure that the bottom of the bowl with your chocolate doesn't touch the water beneath.
Then mix in the egg and vanilla extract into the butter mixture.
Add the flour mixture into the butter mixture. Start with the mixer on a low speed, and gradually mix together until combined.
Turn off the mixer and stir in 1¼ cup chocolate chips.
Cover the bowl with plastic and place in the fridge to chill for at least 3 hours or up to 48 hours.
Once ready to bake, preheat the oven to 375℉ (190℃). Line 2 cookie sheets with parchment paper or a silicone baking mat.
Take the dough out of the fridge. If it's been in the fridge overnight, let it sit on the counter for about 10 minutes first. Then form the dough into balls with about ¼ cup of dough each. I use a kitchen scale for uniform dough balls - each of mine weighed about 3.5 ounces (100 grams).
Place the dough balls 3 inches apart on the lined cookie sheets. Bake 1 sheet at a time in the middle of the oven for 12-14 minutes, or until the tops look just set.
Remove from the oven. For perfectly round cookies, take a large biscuit cutter that is larger in size than the cookies. Place around each cookie, and gently trace a circular shape to mold the cookie into a perfect circle. Cool the cookies completely on the cookie sheet.