Preheat the oven to 325° and line a 9x9 pan with parchment paper. Set aside.
In a small sauce pan over medium heat, melt butter. Once melted, add sugar and stir for 1-2 minutes. Sift in the cocoa powder, stir and let in cool for about 5 minutes.
Pour into a large bowl and add eggs one at a time, mixing well. Add in the vanilla and coffee. Add in the flour, cornstarch, and salt and mix until no flour packets remain.
Fold in the chocolate chunks and pour into prepared pan.
Bake for 25-35 minutes or the center is set. The toothpick test doesn't work well on these brownies because of the chocolate chunks.
Let fully cook before removing from pan and cutting.