To Make the Chocolate Pastry Preheat the oven to 375°F (190°C).Roll the pastry crust into a large circle about ¼-inch (6 mm) thick and line a 9-inch (23 cm) tart pan with a removable bottom. Prick (aka dock) the crust with a fork then line with parchment paper and fill with pie weights. (See How to Blind Bake a Pie Crust)Place the tart pan on a baking sheet to catch any melting butter and blind bake for 15 minutes.Remove the parchment and pie weights, and continue to bake until fully baked, about 5 to 10 minutes more. Set aside to let cool.

To Make the Chocolate FillingPlace the dark and milk chocolate in a heatproof bowl.In a small saucepan, heat the cream, butter, and salt until simmering, then pour the mixture over the chocolate.Let this stand without stirring for 5 minutes, then gently stir until the mixture is smooth.Lastly, stir in the whiskey until combined, then spread evenly into the tart shell.Refrigerate uncovered for at least 2 hours, until firm and set.

To Make the MeringueJust before serving, combine the egg whites, sugar, and cream of tartar in the top of a double boiler over simmering water and whisk until the sugar has melted.Transfer to the bowl of a stand mixer fitted with a whisk attachment (or use a handheld electric mixer) and whip on high speed for about 7 minutes to stiff, glossy peaks.Pile meringue on top of the chilled tart and toast using a kitchen torch. Serve immediately. Store leftovers in the fridge for up to 24 hours.