When adding the top layer of brownie batter, it is best to spoon dollops of the batter over the top of the potato chips. Because the potato chips are loose, they are liable to be picked up and mixed into the batter, which is not the goal. Instead, you want to try to add the brownie layer without too much disturbance. Nudging dollops of brownie dough will be easier than trying to spread out from one place.