S’mores Sandwich Cookies

Preparation

1. Cookies

   Step 1

   Place racks in upper and lower thirds of oven; preheat to 350°. Crumble 15 graham cracker sheets into a food processor and pulse until finely ground (or place crackers in a resealable plastic bag and smash to fine crumbs; you should have about 1¾ cups). Whisk graham cracker crumbs, 1¾ cups (219 g) all-purpose flour, 2 tsp. baking soda, and 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt in a small bowl to combine.

   Step 2

   Beat 1 cup (packed; 200 g) light brown sugar, ¾ cup (1½ sticks) unsalted butter, room temperature, 3 Tbsp. mild-flavored (light) molasses, and 1 Tbsp. vanilla bean paste or vanilla extract in the bowl of a stand mixer fitted with the paddle attachment on medium-high speed, scraping down sides of bowl as needed, until light and fluffy, about 3 minutes. Add 1 large egg, room temperature, and beat until mixture is very light and fluffy (almost like frosting), about 3 minutes more. Turn off motor, add dry ingredients, and mix on low speed just until a soft dough forms.

   Step 3

   Scoop out 2-tablespoonful portions of dough until you have 24; roll into smooth balls. Divide between 2 parchment-lined baking sheets, spacing at least 2" apart, to create a 4x3 grid. Bake cookies, rotating top to bottom and front to back halfway through, until cracked and very lightly browned, 8–10 minutes. Let cool on baking sheets. Repeat with remaining dough to make 8–12 more cookies, placing on a cool baking sheet lined with a fresh sheet of parchment and baking on upper rack.

2. Filling and Assembly

   Step 4

   While the cookies are baking, melt 1½ cups bittersweet chocolate chips (about 9 oz.), 2 Tbsp. unsalted butter, cut into ¼" pieces, ½ tsp. Diamond Crystal or ¼ tsp. Morton kosher salt, and ½ cup water in a small heatproof bowl set over a small saucepan of barely simmering water (do not let the bowl touch the water), stirring occasionally, or melt in a microwave-safe bowl in a microwave in 15-second bursts, stirring to combine between bursts. Let chocolate filling cool slightly.

   Step 5

   Once cookies are done baking, heat broiler. Spread 8 oz. marshmallow crème (about 1½ cups) evenly over an unlined baking sheet. Broil until deeply burnt (top should be almost entirely black), 2–3 minutes. Let cool 5 minutes, then scrape burnt marshmallow crème (and any sugar pooling underneath it) back into jar with remaining 8 oz. marshmallow crème (about 1½ cups). Stir in remaining ½ tsp. Diamond Crystal or ¼ tsp. Morton kosher salt.

   Step 6

   Check chocolate filling; it should be thick like a loose frosting. If it’s too thin, let cool longer. Transfer to a small resealable plastic bag, seal, and cut end off a corner to make about a ¼" opening. Turn over half of the cookies and pipe a border around bottoms. Fill area within border with a generous dollop (about 1 Tbsp.) of the marshmallow mixture and place a plain cookie, right side up, on top, pressing down slightly to adhere.

   Do Ahead: Cookies can be baked 5 days ahead; store airtight at room temperature. Crème pies can be assembled 2 days ahead; wrap tightly and chill.