Preheat oven to 350°F. Line a baking sheet with parchment paper.

In the bowl of a stand mixer, fitted with paddle attachment, beat the butter and sugar together until light and fluffy. Add the egg and vanilla, and continue mixing until smooth, scraping down the sides of the bowl as necessary. Add the flour, graham cracker crumbs, baking powder, salt, and cinnamon, and mix on medium-low speed until just combined. If dough still looks crumbly, use your hands to squish the dough together. Cover and chill in the refrigerator for 1 hour.

Using a small cookie scoop, drop dough about 2-inches apart onto prepared baking sheet. Flatten slightly with your hands. Bake cookies for 9-10 minutes, or until the edges are firm and the centers look slightly glossy. Allow cookies to cool on pan for 5 minutes before transferring to a wire rack to cool completely.

In a microwave-safe bowl, add the chocolate and heavy cream. Microwave for 1 minute. Remove, then whisk together until smooth. Allow to cool and thicken slightly.

Add the egg whites and sugar to a heatproof bowl and set over a saucepan of barely simmering water. Heat mixture, stirring constantly, until the temperature hits 160ºF on a candy thermometer, about 3-5 minutes.

Remove bowl from saucepan, add the cream of tartar, and beat mixture with an electric hand-mixer (or in a stand mixer) on high speed until stiff glossy peaks form, about 5-7 minutes. Add the vanilla near the very end. Transfer filling to a piping bag fitted with a round tip, or a zip-lock bag with the corner cut off.

Pair each cookie up with a cookie that matches its shape and size. Spread chocolate ganache onto the bottom side of one cookie. Pipe marshmallow fluff onto the bottom side of another cookie. Using a mini blow torch (or an oven broiler), toast the marshmallow fluff, then carefully place on top of the ganache-frosted cookie. Repeat with the remaining cookies.

Store in an airtight container in the refrigerator for up to 5 days.