For Graham Cracker Crust
- Preheat oven to 350 degrees. Coat a 6×9-inch pan with nonstick spray.
- Stir together cracker crumbs, sugar, salt, and butter until combined. Press mixture into pan.
- Bake for 8 minutes, then cool completely on wire rack.
For Brownie Center
- In a medium-sized mixing bowl, whisk eggs until frothy and set aside.
- In a large mixing bowl, whisk together flour, cocoa powder, sugar, and salt.
- In a medium saucepan, melt butter over low heat. Remove from heat and add chocolate. Stir until chocolate melts.
- With an electric mixer, beat vanilla and eggs into butter and chocolate mixture. Slowly add liquids to dry ingredients, mixing continuously until no lumps remain. Pour over cooled graham crust.
- Bake in 350-degree oven for 35 minutes or until set
For Marshmallow Topping
- Soften gelatin in large bowl with ¾ cup water and set aside.
- In a small saucepan, combine remaining ¾ cup of water with sugar and corn syrup. Bring to a boil over high heat and cook until syrup reaches 238 degrees on candy thermometer.
- Using a handheld or stand mixer fitted with a whisk attachment, beat mixture on high speed and slowly pour hot syrup into the bowl with gelatin, continuing to mix until very stiff, about 15 minutes.
- Pour mixture over brownies and let cool completely. Refrigerate for 2 hours or until ready to serve. Slice into squares.