01 -
Preheat the oven to 350°F (175°C). Line an 8×8-inch baking pan with foil. Place the graham crackers, sugar, and salt in a food processor and pulse until finely ground. Add the melted butter and pulse until moistened. Press the mixture into the baking pan. Bake for 10 minutes. Cool the pan in the refrigerator while preparing the filling.
02 -
In a small heavy-bottomed saucepan over medium-low heat, combine the chocolate chips and sweetened condensed milk. Stir constantly until melted, thick, and smooth. Pour the mixture over the cooled crust. Chill in the refrigerator while preparing the marshmallow topping.
03 -
In the bowl of an electric mixer with the whisk attachment, beat the egg whites and cream of tartar on medium speed until soft peaks form, about 7 minutes. Meanwhile, in a small saucepan over medium-high heat, combine the granulated sugar, light corn syrup, water, and salt. Bring to a boil and cook until a candy thermometer reads 240°F (115°C), about 8 minutes. Remove from heat and slowly pour the syrup into the egg whites while mixing on low speed. Increase to medium-high speed and beat until thick and fluffy, about 6-7 minutes. Add vanilla extract and beat to combine.
04 -
Spread the marshmallow topping evenly over the fudge layer. Use a kitchen torch to lightly toast the marshmallow topping until golden brown or place the pan under the broiler for about 30 seconds while checking frequently to prevent burning. Refrigerate for at least 1 hour before slicing and serving.