Add the Cheez-its to a large bowl, crush some with your hands, leaving some whole as well. These small crumbs and pieces help the bar keep it's structure. Set aside.

In a 2-quart saucepan over medium-low heat, add the butter. Let the butter melt completely before adding in the 2 bags of marshmallows. Use a nonstick spatula to coat the marshmallows in the melted butter. Stir occasionally to melt marshmallows until they are completely smooth, about 5 minutes. Adjust the heat to low and add in the peanut butter. Stir to combine until the mixture is homogenous. In a large heatproof bowl, or directly in your saucepan if it is big enough, add in just 1/2 of the Cheez-Its, mix until completely coated, then add in the second half. Mix again until all Cheez-Its are coated and press mixture into an 8x8 pan. Let set for at least 20 minutes in the fridge then slice.

If desired, drizzle tops with melted peanut butter!