Preheat the oven to 350°F/176°C. Grease an 8x8 pan and parchment paper and line.
Set a large bowl over a pot with water in it and boil the water. Add 11 oz of the chocolate chips and butter to the bowl and melt, stirring often.
Once fully melted, remove from heat and add the espresso and both sugars. Stir completely. Whisk the eggs in a separate bowl, then add to the chocolate mixture. Stir in the vanilla extract.
In a separate bowl, whisk together the flour, salt, and cocoa powder, then gently stir into the chocolate mixture. Stir until nearly combined, then add about 1/2 cup chocolate chips and stir again until combined.
Pour into the pan and top with chocolate chips.
Bake for 40-50 minutes, until edges are slightly crispy.
Let cool completely, for at least 4 hours, before cutting.