01 -
Line a 20 cm or 23 cm square baking pan with parchment paper, allowing enough overhang for easy removal, and set aside.
02 -
Place chopped chocolate in a bowl. Heat heavy cream in a small saucepan until just simmering, then pour over chocolate. Let sit for 2–3 minutes, then stir gently until smooth and combined. Cover and refrigerate while preparing meringue.
03 -
Combine egg whites, granulated sugar, and cream of tartar in a heatproof bowl. Set bowl over a saucepan with 5 cm gently simmering water, ensuring the bowl does not touch the water. Whisk constantly until sugar dissolves and mixture thins, about 4 minutes. Remove from heat, add vanilla extract, and beat on high speed with a mixer until stiff, glossy peaks form, about 5–6 minutes. Reserve 1 heaped cup of meringue for the topping, cover, and refrigerate.
04 -
Spread a very thin layer of marshmallow meringue in the base of the prepared pan to anchor the first layer. Top with a layer of graham crackers, breaking as needed for a snug fit.
05 -
Spread a layer of meringue over crackers. Add another layer of graham crackers, then a layer of ganache. Continue building in the sequence: graham crackers, meringue, graham crackers, ganache, graham crackers, meringue, graham crackers, and finish with ganache on top. This should yield 6 layers of crackers, 4 layers of meringue, and 3 of ganache.
06 -
Cover pan tightly and refrigerate for at least 12 hours or overnight to allow layers to set.
07 -
Remove reserved meringue from refrigeration and rewhip if necessary. Lift cake from pan using parchment, transfer to a heat-proof surface, and peel away parchment. Spread meringue evenly on top, swirling with a spoon. Toast topping using a kitchen torch until golden.
08 -
Serve immediately, or refrigerate for up to 1 hour before torching toasting meringue. Keep leftovers tightly covered in the fridge or freezer for up to 2 days.