Mix the flour (250g) the cocoa powder (45g), the baking powder (1 tsp) and salt (½ tsp) together in a bowl and whisk or sift together. Set aside.
In a large bowl or the bowl of a stand mixer, cream the butter (142g), white sugar (150g), and brown sugar (100g) together until fluffy. Usually takes a couple of minutes.
Add the egg and vanilla and mix until incorporated.
With the mixer running (see why a stand mixer is helpful?) add the dry ingredients a half-cup at a time and allow to incorporate until you've added all the dry ingredients and a dough has formed.
Remove from the mixer and add the chocolate chunks and chips, incorporating by hand until evenly distributed.
Scrape the bowl out onto a piece of parchment (usually 12" x 19") and roll into a log the width of the parchment. (A silpat sheet may help.) So the log should be around 2" in diameter. Completely roll the parchment around the log and place in your refrigerator for at least two hours.
(two hours pass)
Heat your oven to 325℉ / 160℃.
Line two baking sheets with parchment paper.
Using a sharp knife or bench knife cut off ~⅜-½" slices and arrange on a baking sheet. I got 10 per sheet -- they don't seem to spread a lot during baking.
Bake for 12-15 minutes, turning and swapping racks halfway through. Hard to tell when they're done because they're so dark, so ya gotta kinda take it on faith. I did 7 minutes and 7 minutes and they were done. Still a bit soft in the middle but if you touch the edges they should be firming up.
Let cool out of the oven and on the baking sheet for 3-5 minutes before moving to a cooling rack.