For the marshmallows
1/2 cup plus 1/3 cup room temperature water
2 tablespoons plus 1/2 teaspoon unflavored granular gelatin
2 cups granulated sugar
1/2 cup light corn syrup
1/8 teaspoon salt
2 large egg whites, at room temperature
1/8 teaspoon cream of tartar
1 teaspoon vanilla extract
1/3 cup cornstarch
1/4 cup confectioners’ sugar
For the graham crackers
1/2 cup plus 1 tablespoon all-purpose flour
1/2 cup graham flour
1/2 teaspoon baking soda
1/4 teaspoon salt
4 tablespoons (1/2 stick or 1/4 cup) unsalted butter, softened
1/4 cup plus 1 tablespoon packed dark brown sugar
1 tablespoon honey
1/2 teaspoon vanilla
2 tablespoons milk
For the topping
24 ounces block bittersweet or semisweet chocolate, finely chopped
To prepare the marshmallows
Thoroughly coat a 9" x 13" baking pan with nonstick cooking spray - line the bottom with parchment paper, then spray the top of the paper with additional cooking spray.
In a small bowl, add 1/2 cup water - sprinkle gelatin over the top and set aside to soften.
In a medium saucepan, stir together sugar, corn syrup, water, and salt. Cover saucepan and bring to a boil over medium to medium-high heat - uncover and allow to cook, without stirring, until it reaches 240 degrees (soft-ball stage). Remove from the heat and whisk in the softened gelatin until dissolved. Place the cover back onto the pot and set on the stove, with the burner turned off, to keep warm.
In a large mixing bowl, whisk egg whites on medium speed until frothy. Add cream of tartar - increase speed to medium-high and beat until soft peaks form. Carefully pour the hot syrup gradually down the side of the bowl in a thin stream - keep the speed around medium so the mixture doesn’t splash out of the bowl. When all of the syrup has been added, increase speed to high and beat until the mixture is cool to the touch, very fluffy and stiff, but still pourable, about 8-12 minutes. Beat in the vanilla.
Immediately pour the mixture into the prepared 9" x 13" baking span, spreading with an off-set spatula to fill the pan, smoothing the top as best you can as you go.
In a small bowl, whisk together cornstarch and confectioners’ sugar. Sift mixture lightly over the top of the marshmallows to cover. Set the pan aside until the mixture firms up, at least 8 hours.
Dust the top of a cutting board with the confectioners’ sugar mixture - turn the marshmallows out onto the cutting board and peel away the parchment paper. Dust the marshmallow slab all over with the confectioners’ sugar mixture. Using a thin, sharp knife, slice the marshmallow into forty 1 1/2" squares. If not using the marshmallows immediately, toss them lightly with the confectioners’ sugar mixture to prevent them from sticking together and store in an airtight container, at room temperature, until ready to assemble the cookies.
To prepare the graham crackers
In a medium bowl, whisk together flours, baking soda and salt.
In a large mixing bowl, beat butter until creamy. Beat in sugar and honey until very smooth. Mix in vanilla. Add the dry ingredients in two additions, alternately with the milk, beginning and ending with the flour mixture.
On a lightly floured surface, roll dough to 1/4" thick and cut dough into 1 1/2" squares. Place crackers onto parchment-lined baking sheets. Gently gather remaining scraps, roll out again to cut out as many crackers as possible and transfer them to fill out the baking sheets. Cover and place sheets into the refrigerator while the oven preheats.
Place racks in the upper and lower third of the oven - preheat oven to 350 degrees.
If the marshmallows have been coated with cornstarch, gently shake them to remove any excess coating.
When the oven it heated, place the graham crackers in and bake until the crackers are just dry to the touch, but still have tiny bit of spring to them, about 12 to 14 minutes - do not over-bake.
Remove from the oven and place pans on wire racks - immediately place a marshmallow on top of each cracker, letting the residual heat seal the two together. Let cookies cool completely.
To prepare the chocolate topping
In a heat-safe bowl, gently melt chocolate over a pot of barely simmering water, making sure the bottom of the bowl does not touch the water. Pour chocolate into a narrow, but deep bowl.
Slowly dip the cracker, marshmallow side down, into the chocolate, making sure the chocolate covers the marshmallow completely as well as the sides of the cracker. Pull cracker out and gently shake back and forth to drip off any excess chocolate. Place back onto the pan, cracker side down, and repeat process with remaining crackers
Place pans into the refrigerator briefly to set the chocolate. Remove and store at room temperature until serving.
Makes about 40.