In a medium bowl, sift together cocoa, flour, and baking soda. Whisk in salt. Set aside.

In a small bowl, mix together sugars and molasses. Set aside.

Place chocolate chunks in a strainer and tap the edge to shake out chocolate dust.

In the bowl of a stand mixer fitted with the paddle attachment, beat butter on medium-low until smooth, shiny, and it holds peaks when the beater is lifted.

Add sugar mixture and beat until light and fluffy, about 4 minutes. Scrape down sides of bowl. Add egg and beat on low until just incorporated, 15 seconds.

Add flour mixture in two additions, beating on low until just incorporated, 15 to 20 seconds, and scraping down sides of bowl between additions.

Add chocolate chunks and chips, and pulse mixer about 10 times to incorporate.

Refrigerate 30 minutes.

Preheat oven to 325°F.

Line baking sheets with silicone baking mats or parchment.

Using a 1 1/2 Tbs scoop, portion dough on baking sheets, leaving 1 1/2 inches of space between cookies.

Bake 15 to 17 minutes, rotating top to bottom and front to back halfway through, or until cookies look completely baked.

Cool 10 minutes on sheet, then transfer to a baking rack to cool completely.