Make the crust: Preheat oven to 350°F. Line a 9 inch square baking pan with foil, allowing 2 inches to overhang on two sides. In a medium bowl, using a fork, mix all the ingredients until evenly moistened. Press the crumbs evenly into the bottom of the prepared pan. Bake for 8 - 10 minutes until lightly browned. Let cool completely.

Make the filling: In a heat proof medium bowl set over a saucepan of simmering water, melt the butter with the chocolate over moderate heat, stirring occasionally, until smooth, about 5 minutes. Remove from the heat and whisk the sugar, vanilla and salt. Whisk in the eggs until smooth, then stir in the flour until just incorporated. Spread the batter evenly over the cooled crust. Bake for about 25 minutes until the edge is set but the center is still slightly jiggly. Transfer to a rack and let cool of completely.

Make the meringue : Preheat broiler. In a heat proof medium bowl set over a saucepan of simmering water, whisk the egg whites with the sugar until the whites are warm and sugar is dissolved about 3 minutes. Transfer egg whites to a bowl in a stand mixer fitted with a whisk. Add the vanilla and cream of tartar and beat at medium speed until firm. Increase the speed to high and beat the meringue until stiff and glossy. 5 to 7 minutes.