Preheat oven to 350F. Grease a loaf pan or 8x8inch baking dish with cooking spray. Brownies will be thicker with a loaf pan.
Place all ingredients except chocolate chips in a large bowl. If your nut butter is unsalted, add an additional ¼ tsp salt. Whisk until well combined. Fold in chocolate chips. The batter is very thick.
Spoon mixture into loaf pan and use a rubber spatula to spread evenly in pan. Sprinkle with a handful of chocolate chips and a pinch of flaky salt.
Bake for 25-30 minutes, or until brownies are set and a knife comes out almost clean. If your peanut butter wasn't liquidy/drippy, they will take less time.
Sprinkle brownies with flaky salt. Allow to completely cool before slicing. Slice into 9 bars for a square pan or 10 bars for a loaf pan. I like these best after they've chilled overnight in the fridge!
