CRUST:
- 20 full graham crackers
- 1/4 cup granulated sugar
- 1/2 teaspoon cinnamon
- 1/2 teaspoon salt
- 12 tablespoons unsalted butter, melted
FUDGE FILLING:
- 2 cups semisweet chocolate chips
- 1 (14 ounce) can sweetened condensed milk
MARSHMALLOW TOPPING:
- 2 large egg whites
- 1/4 teaspoon cream of tartar
- 3/4 cup granulated sugar
- 1/2 cup light corn syrup
- 1/4 cup water
- 1/4 teaspoon salt
- 2 teaspoons vanilla extract
FOR THE CRUST:
- Preheat oven to 350°F. Line an 8×8-inch baking pan with foil, set aside.
- Combine graham crackers, sugar, cinnamon, and salt in the bowl of a food processor and pulse until finely ground. Add melted butter and pulse until mixture is moistened.
- Press mixture into the bottom of prepared baking pan and bake for 10 minutes. Remove to a cooling rack and let cool completely.
FOR THE FILLING:
- Combine chocolate chips and condensed milk in a small saucepan set over medium-low heat. Cook until mixture is melted, thick, and smooth, stirring constantly.
- Pour over graham cracker crust. Place in the refrigerator while making the marshmallow topping.
FOR THE MARSHMALLOW TOPPING:
- In the bowl of an electric mixer fitted with the whisk attachment (or use a hand mixer and large bowl), beat the egg whites and cream of tartar until soft peaks form. Set aside.
- Combine sugar, corn syrup, water, and salt in a small saucepan set over medium-high heat. Bring the mixture to a boil and continue to cook until a candy thermometer registers exactly 240°F. Immediately remove from heat.
- Start beating the egg whites again, on low speed, while carefully pouring the corn syrup mixture into the bowl.
- Increase speed to medium-high and beat until the mixture is thick and glossy and looks like marshmallow fluff, about 7 minutes. Add in the vanilla and beat until combined.
- Spread marshmallow topping evenly over chocolate fudge layer. Optional: Place the pan under the broiler and broil for 1 minute, or until lightly golden.
- Refrigerate for at least 1 hour before cutting into squares and serving. The squares can be stored in an airtight container in the refrigerator for up to 5 days.