Line a 9x13 pan with parchment paper, then lightly butter the paper and sides of pan. Set aside.
Add sugars to the bowl of a stand mixer with a whisk attachment.
Add cubed butter to a saucepan and begin melting. Turn off the heat when it is mostly melted but there are still chunks. Then, add melted butter to sugar in the bowl of a stand mixer. Whip until it becomes the texture of caramel (about 3-5 minutes).
Melt chocolate chips in the same saucepan on the stove. Allow to cool slightly. Then, drizzle chocolate into bowl of the stand mixer, while it runs on low speed. Incorporate completely.
Stream in the espresso and vanilla.
One at a time, incorporate the eggs completely.
Sift together the flour, cocoa powder, and salt. Incorporate one-third of dry mix into the batter at a time. Once it's all in, turn the speed up to medium-high and beat the batter for 2 minutes.
Spread the batter into the pan.
For a crackly top, bake for 15 minutes. Remove from the oven and jiggle it around to break up top layer. Bake for an additional 10 minutes.
Otherwise, just bake for 25 minutes. A toothpick inserted in the center should come out with moist crumbs.
Allow to cool in the pan for 15 minutes, then remove to a cutting board to finish cooling. Slice into 24 bars.