Start by preheating your oven to 375 degrees F. This is an essential step to ensure that your cookies bake evenly.
Next, line a baking sheet with parchment paper. This will prevent the cookies from sticking and make for easy cleanup.
In a large mixing bowl, cream together ¾ cup butter, ½ cup granulated sugar, and ½ cup light brown sugar for about 2 to 3 minutes. You want the mixture to be light and fluffy, which will help create a tender cookie.
Add the egg, egg yolk, and 1 teaspoon vanilla extract to the creamed mixture. Mix well until everything is fully incorporated.
Now it's time to add the dry ingredients. Gradually mix in 1 ¾ cups all-purpose flour, 1 cup graham cracker crumbs, ½ teaspoon baking soda, and ½ teaspoon salt. Combine until everything is just mixed; you don't want to overwork the dough.
Gently fold in 1 cup semi-sweet chocolate chips. This is where the magic begins, as the chocolate will melt beautifully as the cookies bake.
Chill the dough in the refrigerator for about 15 minutes. Chilling helps the cookies maintain their shape while baking, leading to a thicker cookie.
Once chilled, scoop the dough into 2 tablespoon-sized balls and place them on the prepared baking sheet a few inches apart. This allows room for spreading as they bake.
Press down slightly on each cookie ball to flatten them a bit. This will help them bake evenly.
Bake the cookies for 8 minutes until the edges are lightly golden. They may look slightly underbaked, but they'll continue to cook on the baking sheet.
Remove the cookies from the oven and gently press 2 to 3 small pieces of Hershey's chocolate and 2 to 3 mini marshmallows on top of each cookie. This step adds that classic s'mores touch!
Return the cookies to the oven for an additional 3 to 5 minutes until the marshmallows are slightly toasted and the chocolate is melty.
Finally, allow the cookies to cool on the baking sheet for about 5 minutes before transferring them to a wire rack to cool completely. This step is crucial as it helps them firm up.
