Preparation

• Place an oven rack in the middle position and preheat oven to 350 degrees. Lightly butter or spray a 9-inch pie pan.
• Stir together the butter, graham cracker crumbs, 2 tablespoons sugar and 1/8 teaspoon salt in a bowl until combined. Press the mixture evenly on the bottom and up the sides of the pie pan. Bake 12 to 15 minutes, then cool to room temperature, at least 45 minutes.
• Meanwhile, in a heavy saucepan, bring the cream just to a boil over medium-high heat, then turn remove from the burner and add the chocolate. Let stand 1 minute, then gently whisk until the chocolate is melted and mixture is smooth. Gently whisk in the egg until combined. Pour the mixture into the prepared crust.
• Cover the edges of pie with foil and bake 25 minutes, until the filling is just set and trembles slightly in center when gently shaken. Let the pie cool to room temperature on a rack (filling will firm as it cools), about 1 hour.
• Position a rack in the top third of the oven and preheat to 400 degrees.
• Using rubber spatula, scrape the marshmallow creme into large bowl. Set aside. Using an electric mixer, beat the egg whites and remaining 1/8 teaspoon salt in another large bowl until foamy. Add the remaining 2 tablespoons sugar, 1 tablespoon at a time, and beat until stiff and glossy peaks form.
• Add ½ cup beaten egg whites to the marshmallow creme and fold with a rubber spatula or spoon just until incorporated to lighten (marshmallow creme is very sticky and will be difficult to blend at first, but it will become easier as remaining whites are folded in). Fold in the remaining whites in 2 additions just until incorporated. Spread the meringue over top of pie, mounding slightly in center and swirling with knife to create peaks.
• Bake just until the peaks and ridges of marshmallow meringue are lightly browned, about 4 minutes. Let stand at room temperature until meringue is cool. Serve immediately. The pie will keep up to 4 days, refrigerated, before adding the meringue topping.