Preheat your oven to 350°F (175°C). This is the perfect temperature for achieving a golden, chewy texture.
Grease a 9x13 inch baking pan with cooking spray or line it with parchment paper for easy removal of the bars later.
In a large mixing bowl, combine the all-purpose flour, light brown sugar, baking powder, and baking soda. Mix well. In another bowl, whisk together the melted butter, egg, and vanilla extract until smooth. Gradually incorporate the wet ingredients into the dry ingredients, mixing until just combined.
Pour the cookie base into the prepared baking pan and spread it evenly using your spatula. Bake in the preheated oven for about 15-20 minutes, or until the edges are lightly golden. Allow it to cool slightly while you prepare the topping.
In a double boiler or microwave-safe bowl, melt the remaining ½ cup of unsalted butter along with the peanut butter chips and light corn syrup. Stir until smooth and creamy. Add in the miniature marshmallows, salted peanuts, and Rice Krispies cereal. Gently fold until everything is well combined.
Once the cookie base has cooled slightly, pour the peanut butter and marshmallow mixture over the top, spreading it evenly with your spatula. If desired, sprinkle with flaky sea salt for an extra burst of flavor.
Allow the bars to cool completely at room temperature. Once set, use a sharp knife to cut them into squares or rectangles. Enjoy your homemade Salted Nut Roll Bars!
