Preheat oven to 275°. Line a baking sheet with either parchment paper or a silicon mat. But cornflakes in a bag and crush with a rolling pin. Melt butter and peanut butter in a microwavable bowl.
In a medium sized mixing bowl, mix together the crushed cornflakes, granulated sugar, powdered milk, and salt.
Pour in melted butter over cornflake mixture and toss to combine. It is okay if the cornflakes form littler clusters.
Pour mixture onto prepared baking sheet and bake for 20 minutes or until the mixture is slightly toasted.
Cool completely and break up any larger clusters into little bits.
For the bars
Preheat oven to 350°. Spray a 9x13 baking pan with non stick spray and set aside.
In a large mixing bowl, with an electric mixer on medium speed cream butter and both sugars until smooth. Add large egg and vanilla extract. Mix for an additional 8-9 minutes to allow air into the dough.
Add in both flours, baking soda and powder, and salt and mix on low just until it is combined. Fold in cornflake crunch.
Divide the dough in half and place half of it on the bottom of the greased pan. Press down into an even layer. Top it with semi-sweet, butterscotch chips, and marshmallows.
Cover the rest with the rest of the dough in an even layer on top and extend all the way to the edges. Bake for 25-30 minutes or until golden brown. Cool before cutting and serving!