Drizzle the warm caramel sauce evenly over the tops of both pans of brownie batter. You don’t have to cover every inch—little ribbons and puddles are perfect.
In a medium bowl, stir together the crushed crunchy topping (cornflakes, crisp rice cereal, or pretzels) and the chocolate chips. Sprinkle this mixture evenly over both pans, covering the caramel and brownie batter.
Bake the trays on the middle rack of your oven for the time recommended on the brownie mix box, usually 20–30 minutes. Start checking a few minutes early; you want the edges set and a toothpick inserted into the brownie (not a caramel pocket) to come out with a few moist crumbs but not wet batter.
Remove the trays from the oven and let them cool on a wire rack. The caramel and topping will firm up as they cool, which makes them much easier to slice. If you want cleaner squares, let them cool completely or even chill them briefly in the fridge.
