Step 1

Preheat oven to 350°F. Line a 9x13 inch baking dish with parchment paper and set aside.

Step 2

Cream butter and sugar together in a large mixing bowl. Add peanut butter and continue mixing.

Step 3

Add eggs one at a time, mixing well after each egg. Add in vanilla extract.

Step 4

Combine flour, graham cracker crumbs, oats, cornstarch, baking powder, and salt in a small mixing bowl. Whisk to combine.

Step 5

Add the flour mixture to the butter mixture, slowly stirring until well combined.

Step 6

Stir in the peanut butter chips.

Step 7

Refrigerate cookie dough for at least 30 minutes.

Step 8

Spread 2/3 of the dough on the bottom of the pan.

Step 9

Top with Hershey's bars, breaking apart as needed.

Step 10

Spread marshmallow fluff on top of Hershey's bars.

Step 11

Stir chopped Reese's into remaining cookie dough.

Step 12

Drop the remaining dough on top by the teaspoon. It doesn't have to be perfect and it won't cover all the marshmallow fluff.

Step 13

Bake for 25-30 minutes. Let cool completely and then cut into bars.