1. Preheat the oven to 325°F. Line a 9×13- inch baking pan with foil, and coat with nonstick spray. Set aside.
2. In a medium saucepan, combine the semisweet chips, milk chocolate chips, and butter and melt over medium-low heat, stirring constantly. Once the chocolate is melted, remove the pan from the heat immediately.
3. Whisk both the sugars into the chocolate and add the eggs, one at a time, whisking constantly, until evenly combined. Next mix in the vanilla until smooth. Stir in the salt and flour until they’re evenly incorporated and pour the batter into the prepared pan.
4. Bake the brownies for 35-40 minutes, until the center is set and a toothpick inserted 3 inches from the edge comes out clean. Remove from the oven, and turn the oven to broil.
5. Immediately sprinkle the mini marshmallows on top of the brownies.
6. Return the brownies back into the oven on the top shelf for 30 seconds – 1 minute, or until the marshmallows are lightly golden. Watch carefully as they will burn quickly.
7. Allow the brownies to cool in the pan on a wire rack while you prepare the topping.

Peanut Butter S’mores Layer

1. Cook the corn syrup and sugar together in a large saucepan over medium heat, stirring to dissolve the sugar. Bring the mixture to a boil. Remove from the heat. Stir in the peanut butter; mix well.
2. Fold in the cereal, until coated. Then stir in3/4 cup of the semisweet chips. They will melt slightly, this is ok.
3. Spread the mixture on top of the marshmallows, and sprinkle with the remaining chocolate chips.
4. Allow the brownies to cool completely before cutting into bars.