These cookies taste just like a s'more, no campfire required. The graham crackers really come through in the cookie, while the melty chocolate melds with toasted marshmallow during the baking process.
Whisk together flour, cracker crumbs, baking powder, salt, and baking soda in a medium bowl. Set aside.
Beat together butter, brown sugar, and granulated sugar with a stand mixer at medium-high speed until very light and fluffy, about 5 minutes. Add eggs, 1 at a time, beating to incorporate. After adding both eggs, continue to beat until very whipped, 3 to 4 minutes. Add vanilla.
Reduce speed to low, and gradually add flour mixture to butter mixture. Beat until combined, about 10 seconds.
Scoop cookies with a 1 1/2-inch scoop about 2 inches apart onto a baking sheet lined with parchment paper. Flatten cookies slightly, and press a chocolate piece into each cookie. Top each with a halved marshmallow. Cover baking sheets with plastic wrap, and chill at least 24 hours, and up to 48 hours (or alternatively, freeze about 15 minutes).
Preheat a convection oven to 450°F (or a conventional oven to 425°F). Bake cookies in preheated oven on lined baking sheets until puffed and golden and marshmallow is browned, about 7 minutes. Let cookies stand about 5 minutes before transferring to a wire rack to cool until set, about 5 more minutes.