Preheat the oven to 350. Line a 9 x 9 inch baking pan with enough parchment to overhand the sides.
In a food processor, whip the black beans, coconut oil, maple syrup, instant coffee (if using) and vanilla until very smooth. Bits of black bean skin are okay, just no chunks.
In a large bowl, vigorously whisk the eggs until frothy and bubbly, about 1-2 minutes. Mix in the black bean mixture, then the cocoa powder and salt until just combined. Fold in the chocolate chips.
Pour half of the batter in the prepared cake pan. Dollop spoonfuls of peanut butter on the batter and swirl with a knife until fairly evenly distributed. No need to be perfect. Spread the remaining batter overtop. It's ok if some peanut butter peeks out.
Bake 30-35 minutes until the center is set and an inserted toothpick emerges mostly clean. Remove from the oven and cool 20 minutes in the pan, then lift the parchment carefully and set on a wire rack to cool completely. Alternatively, you can place the whole pan with the brownies in the freezer for 15 minutes to expedite cooling.
When the brownies are cooled, beat together the cocoa powder, maple syrup, coconut oil, vanilla, and salt for the icing. Spread the icing over the brownies with a spatula. Top with chopped peanut butter cups. Set in the fridge for 15 minutes to harden the icing, then cut into 12-16 squares and serve.