• Position the oven rack in the middle of the oven and preheat the oven to 350F [180C]. Grease a 9 by 13 in [23 by 33 cm] baking pan and line with a parchment sling.

For the scotcharoo crunch

• In a large, heavy-bottom saucepan over medium heat, melt the peanut butter, corn syrup, and butter. Add the butterscotch chips and stir until smooth (this will take a few minutes). Remove from the heat and pour the cereal into the hot mixture and use a spatula to stir until completely combined.
• Pour the mixture into the prepared pan and press it down into the pan in a compact layer, making sure the top is smooth. Set aside while you make the blondie batter.

For the blondies

• In a medium saucepan over medium heat, melt the butter, brown sugar, and salt. Remove from the heat and stir in the vanilla. Let the mixture cool to room temperature. Add the egg and baking powder and whisk to combine. Add the flour and use a spatula to stir until just combined. Add the chopped chocolate and stir again until the chocolate is evenly distributed. Pour the batter over the peanut butter crunch layer and use an offset spatula to spread it evenly over the top. The batter will be very thick and will be a little hard to spread - just go slow. It will seem like just a thin layer across the top, but it will puff up nicely in the oven.
• Bake for 22 to 26 minutes, until the blondies are set on the edges, the top is golden brown and just beginning to form cracks, and a wooden skewer or toothpick inserted into the center comes out with just a couple of crumbs. Transfer the pan to a wire rack and let cool completely. Use the parchment sling to gently lift the blondies from the pan. Cut into squares and serve. The blondies can be stored in an airtight container for up to 2 days.