Step 1

Preheat oven to 275°F and line a baking sheet with parchment paper.

Step 2

In a large bowl mix together the crushed cornflakes, powdered milk, granulated sugar, and salt.

Step 3

Pour in the melted butter, tossing to combine, forming small clusters.

Step 4

Spread evenly onto a baking sheet and cook until the cereal is slightly toasted, about 15 to 20 minutes.

Step 5

Cool completely and then break up into large clusters.

Step 6

Preheat oven to 350°F, line a 8x8 baking pan with parchment paper and grease with butter, and set aside.

Step 7

In a large bowl, whisk flour, salt, baking powder, and baking soda, set aside.

Step 8

With a mixer cream butter, granulated sugar, and light brown sugar until light and fluffy, about 3 minutes on medium speed.

Step 9

Add egg and vanilla and continue to beat for 8 minutes. This will aerate the batter.

Step 10

Lower the speed of the mixer and slowly add dry ingredients, mixing until just incorporated.

Step 11

Use a rubber spatula to gently fold in the cooled crunch-mixture.

Step 12

Divide the dough in half. Press one half into the prepared pan.

Step 13

Cover with chocolate and marshmallows.

Step 14

Top with remaining dough, pressing into an even layer and to the edges of the pan.

Step 15

Bake until golden brown, about 25 to 30 minutes.

Step 16

Let the bars cool completely before slicing and serving.