Preheat oven to 350°F. Spray a regular sized muffin tin with cooking spray.
Whisk together flour, graham cracker crumbs, baking soda, and salt, set aside.
Beat butter and sugars on med-high until light and fluffy (approx. 2-3mins). Reduce speed and add egg and vanilla. Beat until combined. Add flour mixture and mix until just combined.
Using a large cookie scoop (3 Tbsp) scoop dough into muffin tins, press down to flatten.
Bake for approx. 13mins or until browned and mostly set.
Remove from oven and immediately use a small jar or container to press firmly down in the center to create a well. Cool in pans for 15mins, then place on wire rack to cool completely.
Place chopped chocolate and cream into a microwave safe bowl. Stir to combine. Microwave for 20 seconds, stir. Microwave in 10 second intervals, stirring in between, until smooth and silky. Set aside to cool completely before using.
Place water, sugar, and corn syrup (or honey) in a medium saucepan. Stir to combine.
Insert a candy thermometer into the pot and heat over medium-high. Do not stir from this point on as crystals will form.
Ensure mixer bowl and whisk are completely grease free.*
Place egg whites and cream of tartar in the bowl of a stand mixer.
When the sugar syrup reaches about 225°F, start whipping the egg whites to soft peaks. Approx 3-4mins.
When the whites are ready, the sugar syrup should be at 240°F. Remove from the heat, turn mixer to medium and very slowly and carefully pour the sugar syrup into the whites in a thin, steady stream.**
Once all of the syrup is in, set mixer to medium/high and continue whipping. The whites will deflate at first, but they will thicken and fluff up. Continue to whip for 7-8 minutes, or until the mixture is thick and glossy. Add in vanilla and whip until the fluff has cooled.
Pour chocolate onto a liquid measuring cup for ease. Pour a couple of teaspoons of chocolate into each cookie cup. Allow to set (you can speed this up in the fridge).
Prepare a large (16) piping bag fitted with a large round tip (I used Ateco 808). Fill with marshmallow fluff and pipe onto each cookie cup. Toast with a kitchen torch.
*If there is even a speck of grease (or egg yolk) the meringue will not whip. I wipe everything down with lemon juice before adding the egg whites.**The sweet spot for this is getting the stream right between the whisk and the sides of the bowl, so the syrup doesn't get splashed by the whisk. You will have some marshmallow fluff left over which you can store in an airtight container in the freezer and use it at a later date for S'mores Macarons, S'mores Baked Alaska, or good old Rice Krispie Treats.