Dough Preparation

• Start by preheating your oven to 350°F (175°C) and lining an 8×8 inch square pan with parchment paper.

  In a large bowl, cream the softened butter with brown sugar and granulated sugar until the mixture is light and fluffy. This gives your cookie base that rich caramelized flavor. Next, add in the egg and vanilla extract, beating until well combined.

  Then, fold in the dry ingredients: flour, finely crushed graham crackers, baking soda, and salt. Mix just until the dough comes together and you can no longer see streaks of flour. Be careful not to overmix—this ensures the bars stay soft and chewy.
• After your dough is ready, divide it into two equal portions. Press the first half evenly into the parchment-lined 8×8 baking pan. This will form the sturdy base for your bars.

  Now, carefully lift the parchment paper with the pressed dough out of the pan and place it in the freezer. This firms it up so you can later place it on top without breaking it.

  While that bottom layer chills, re-line the same pan with a fresh sheet of parchment paper, and press the remaining cookie dough into the pan. This will now become your top layer once we assemble everything.
• Once your top dough layer is pressed into the pan, it’s time to lay down the chocolate bars. Place the Hershey bars directly over the dough—feel free to break them apart if needed to cover the surface evenly.

  Next comes the best part: spoon the marshmallow fluff right over the chocolate layer. Use a rubber spatula or spoon to gently spread it across the chocolate. It doesn’t have to be perfect—once it bakes, it will melt beautifully.
• Now, go back to your freezer and carefully remove the chilled bottom dough layer from the parchment. Flip it on top of the marshmallow layer, lining it up as best as you can. If it breaks slightly, no worries—just patch it together by pressing gently.
• Preheat your oven to 350°F (175°C) if you haven’t already.

  Place the assembled pan in the center rack and bake for about 25 minutes. The top should be a light golden brown, and you may see some marshmallow fluff peeking through the edges—that’s a good sign!

  Avoid overbaking, as you want the bars to remain soft and gooey in the center. Once done, remove the pan from the oven and set it on a cooling rack.
• This part requires a little patience (I know—it’s tough). Let the bars cool completely in the pan before slicing. If you cut them too soon, the layers may slide or collapse, and you'll miss out on that clean, picture-perfect cross-section.

  Once cooled, use the parchment paper to lift the entire slab out of the pan, and place it on a cutting board. Use a sharp knife to slice into squares or rectangles—whatever shape your cookie-loving heart desires.