7–8 graham cracker sheets (78–109 g total)

1 cup (226 g) unsalted butter, room temperature (2 sticks)

¾ cup (150 g) granulated sugar

¾ cup (150 g) light brown sugar, gently packed

2 large eggs

2 tsp vanilla extract

3 cups (360 g) all‑purpose flour

¾ tsp salt

¾ tsp baking soda

½ cup (135 g) semi‑sweet chocolate chips

1 cup (45 g) mini marshmallows

2 Hershey’s Milk Chocolate bars (1.55 oz/43 g each), broken into squares

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Preheat oven to 375 °F. Line a 13×9-inch pan with parchment paper, leaving about 2-inch overhang on the sides.
Arrange graham crackers to cover the bottom of the pan, breaking as needed to fill gaps.
In a mixer fitted with the paddle attachment, cream together butter, granulated sugar, and brown sugar until light and fluffy.
Add eggs and vanilla; mix and scrape bowl to combine.
In a separate bowl, whisk together flour, salt, and baking soda.
Add the dry mixture, chocolate chips, and mini marshmallows to the butter mixture. Mix until just combined—don’t overmix.
Spread the cookie dough evenly over graham crackers and gently press flat. Optionally, sprinkle extra mini marshmallows on top.
Bake at 375 °F for 25–30 minutes, until golden brown and a toothpick from the center comes out clean. If the edges brown too quickly, tent with foil.
Remove from oven and immediately press the chocolate bar squares on top. Let cool 20–30 minutes before lifting out using parchment overhang.
Serve warm or at room temperature.

Store at room temperature in an airtight container or covered baking pan for up to 3 days.
Reheat a bar in the microwave for 10–15 seconds for gooey texture.
Use a metal or aluminum pan for more even baking.
Can be made with a gluten-free flour blend 1:1.
Use dairy-free butter and vegan marshmallows for dairy-free version.
Chill bars before slicing for clean cuts.
Freeze individually wrapped bars for up to 2 months.