Step 1: Preheat oven to 350°F (175°C). Line an 8×8 or 9×9-inch baking pan with parchment paper, leaving an overhang, and lightly grease.
Step 2: For the graham cracker crust, combine crumbs, melted butter, and 2 tbsp sugar. Press into the pan. Bake 8-10 minutes. Set aside.
Step 3: In a double boiler, melt 1 cup butter and chopped dark chocolate, stirring until smooth. Remove from heat; cool slightly.
Step 4: In a large bowl, whisk 1 ½ cups granulated sugar, brown sugar, and eggs until light and fluffy (2-3 min). Stir in 1 tsp vanilla extract.
Step 5: Gradually add cooled chocolate mixture to egg mixture, mixing until just combined.
Step 6: Sift together flour, cocoa powder, and ½ tsp salt. Gently fold into wet ingredients until just combined.
Step 7: Pour batter over crust. Bake 25-30 minutes, or until a toothpick comes out with moist crumbs. Cool completely in pan.
Step 8: For marshmallow, sprinkle gelatin over ½ cup cold water in a stand mixer bowl. Let bloom 5-10 minutes.
Step 9: In a saucepan, combine 1 ½ cups sugar, corn syrup, ¼ cup water, and pinch of salt. Add vanilla bean seeds and scraped pod.
Step 10: Cook over medium-high heat, stirring until sugar dissolves. Once boiling, stop stirring and cook until syrup reaches 240°F (115°C).
Step 11: Remove vanilla bean pod. With mixer on low, slowly pour hot syrup into bloomed gelatin. Increase speed to high; beat 10-12 minutes until thick, glossy, and stiff peaks form.
Step 12: Spread marshmallow topping evenly over cooled brownies.
Step 13: Toast marshmallow with a kitchen torch or under a broiler (watch closely, 1-2 min).
Step 14: Sprinkle with extra crushed graham crackers. Cool slightly before slicing.