For the crust: Pulse the graham crackers in a food processor or crush in a resealable plastic bag until they are fine crumbs. Add the crumbs to a bowl and stir in the melted butter and sugar. Press the mixture into a pie pan and bake until set, about 4 minutes. Set aside and allow to cool completely.
For the filling: Stir together the cornstarch, sugar and salt in a large saucepan over medium heat. Pour in the milk and beaten egg yolks. Cook, stirring, until the mixture comes to a boil. Remove from the heat and stir in the chocolate, butter and vanilla. Pour the chocolate filling into the cooled shell until it's filled to the brim. (You may have some left over.) Smooth the top of the pie, then gently press a piece of wax paper over the filling and chill until set, 3 to 4 hours. Store any leftover filling covered in the fridge for another use or snacking.
For the meringue: Add the sugar, corn syrup, 2 tablespoons water and a pinch of salt in a saucepan over medium heat. Cook, stirring, until the sugar has dissolved completely. Remove from the heat.
Add the egg whites to the bowl of an electric mixer. Beat the egg whites on medium speed until frothy, about 1 minute. Add the cream of tartar and the remaining pinch salt and continue beating for 30 seconds. With the machine running on medium speed, drizzle the hot syrup mixture into the mixing bowl in a constant stream, then turn the speed to high and whip until the mixture forms stiff peaks (about 3 minutes).
Remove the chilled pie from the fridge and discard the wax paper. Spread the meringue over the top of the chilled pie, making sure to get it to the edges. With the back of a spoon, lightly press into the meringue, lifting the spoon away, to create peaks. Toast the meringue with a brulee torch to the desired color. Slice and serve.
Propane gas torches are highly flammable and should be kept away from heat, open flame and prolonged exposure to sunlight. They should be used only in well-ventilated areas. Follow torch manufacturer's instructions for use.