Preheat oven to 350°F. Line 13×9 pan.
Heat butter + sugar until melted, cook 1–2 min. Remove from heat, stir in chocolate + cocoa.
Cool slightly, then mix in discard, eggs, vanilla.
Sift in flour, salt, espresso, baking powder. Stir to combine; fold in chocolate chips.
Spread in pan, bake 22–28 min (edges set, center 185–198°F).