Preheat your oven to 175°C (350°F) and line a 20 cm square baking pan with parchment paper.

In a heatproof bowl over a simmering water bath, melt together the unsalted butter and chopped dark chocolate until smooth.

Stir in the granulated sugar until combined, then add eggs one at a time, mixing until glossy. Add vanilla extract and mix until smooth.

Sift in all-purpose flour, unsweetened cocoa powder, and salt; fold gently until just combined.

Fold in crushed graham crackers, then pour the batter into the prepared baking pan and smooth the top.

Bake for 20–25 minutes. The edges should set firmly and the center should be slightly fudgy. Let cool completely in the pan.

In a small bowl, combine cold water with powdered gelatin and let it bloom for 5 minutes.

In a saucepan, heat granulated sugar, light corn syrup, and water until it reaches 115°C.

Whip egg whites until soft peaks form, then gradually drizzle in the hot syrup and whip until stiff peaks form.

Fold in vanilla bean seeds, then spread the marshmallow topping over the cooled brownie base.

Toast the marshmallow layer with a kitchen torch or broiler until golden brown, being careful not to burn.

Let the marshmallow set for 10 minutes before lifting brownies out of the pan and slicing into squares.