Cookie Cups: Preheat the oven to 350 °F. Grease a standard muffin pan.
In a bowl, whisk flour, graham crumbs, baking soda, and salt. Set aside.
Cream butter and sugars till fluffy (2–3 min), then mix in egg and vanilla.
Add dry ingredients until just combined.
Scoop dough (≈3 Tbsp each) into muffin tin, flatten gently.
Bake until lightly golden and set (~13 min). While hot, press cup indentations with a jar. Cool 15 min, then remove to rack.
Ganache Filling: Melt chocolate and cream until smooth; let cool to barely warm.
Marshmallow Fluff: Combine water, sugar, corn syrup; heat with candy thermometer. Whip egg whites with cream of tartar while syrup heats. When syrup hits ~240 °F, stream into whipped whites, then whip until thick, glossy, and cool. Add vanilla.
Assembly: Spoon ganache into each cup, let set. Pipe fluff on top, then toast carefully with a kitchen torch.