Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper and set aside.

In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy. This should take about 2 minutes using an electric mixer.

Mix in the egg and vanilla extract until well combined, scraping down the sides of the bowl as needed.

In a separate bowl, whisk together the all-purpose flour, graham cracker crumbs, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Gently fold in the chocolate chips and mini marshmallows, ensuring they are evenly distributed throughout the dough.

Using a tablespoon or cookie scoop, drop rounded spoonfuls of dough onto the prepared baking sheet, spacing them about 2 inches apart.

Bake in the preheated oven for 10-12 minutes, or until the cookies are golden brown around the edges but still soft in the center.

Allow the cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.

These cookies are best enjoyed warm, straight from the oven or after a gentle reheating. Serve with a glass of milk or hot cocoa for a classic pairing.

Store leftover cookies in an airtight container at room temperature for up to 5 days. For longer storage, freeze the cookies in a single layer and thaw at room temperature before serving.