In a small bowl, stir together the dulce de leche and salt until combined. Spread a generous, even layer into the bottom of your cooled crust. Set aside.
In a microwave safe, medium bowl, heat the heavy cream until boiling in the microwave. Pour in the bittersweet chocolate, vanilla extract, and salt. Let it sit for a couple of minutes to allow the chocolate to start melting, and then whisk until completely smooth. Pour over the dulce layer in the tart crust. Cover with plastic wrap, laying the plastic directly onto the chocolate layer, and chill for at least an hour.
In a large heat-safe bowl over a double-boiler, whisk the egg whites, cream of tartar, and sugar for about 5-8 minutes, or until the sugar is dissolved. Transfer to a stand mixer, and whisk on medium speed for 10-15 minutes, or until the mixture is cool, and has stiff peaks. Beat in the vanilla and salt.
Pile the meringue on top of the chilled pie, and use a fork to fluff the meringue and create peaks. Use a torch to toast the top of the meringue, or place the pie under a broiler in the oven for 2-3 minutes until it has become toasted. Enjoy!