Preheat the oven to 350° F. Line two baking sheets with parchment paper.
In a large mixing bowl, beat the butter, brown sugar, and granulated sugar until light and fluffy, about 2–3 minutes.
1 cup unsalted butter, 1 cup packed brown sugar, 1/2 cup granulated sugar
Add the eggs and vanilla extract. Mix until well combined.
2 large eggs, 2 teaspoons vanilla extract
In a separate bowl, whisk together the flour, baking soda, and salt.
2 3/4 cups all-purpose flour, 1 teaspoon baking soda, 1/2 teaspoon salt
Gradually add the dry ingredients to the wet ingredients, mixing just until combined.
Fold in the chocolate chips, mini marshmallows, and graham cracker pieces.
1 1/2 cups semi-sweet chocolate chips, 1 1/2 cups mini marshmallows, 8 graham cracker sheets