Preheat your oven to 350°F (175°C) and line an 8x8-inch baking pan with aluminum foil, allowing some overhang for easy removal later.

In a food processor, blend graham crackers, granulated sugar, and fine sea salt until they resemble fine crumbs. Pour in melted unsalted butter and pulse until moistened. Press into the bottom of the prepared pan and bake for 10 minutes.

Let the crust cool slightly, then transfer the pan to the refrigerator to chill for about 20 minutes.

In a medium saucepan over low heat, combine semisweet chocolate chips and sweetened condensed milk. Stir until smooth and melted.

Pour and spread the chocolate fudge mixture over the chilled crust, ensuring an even layer.

In a mixing bowl, beat egg whites and cream of tartar on medium speed until soft peaks form, about 2-3 minutes.

In a small saucepan, combine granulated sugar, corn syrup, water, and a pinch of salt. Heat until it reaches 240°F (115°C) and drizzle into the egg whites while mixing on low speed.

Increase the speed to high and beat until thick and resembles fluffy marshmallow, about 5-7 minutes. Add vanilla extract and beat until combined.

Lightly toast the marshmallow topping with a kitchen torch until golden brown.

Let cool at room temperature for about 10-15 minutes, then refrigerate for at least 1 hour to set. Cut into squares to serve.