Preheat your oven to 350°F (175°C). In a medium bowl, combine the vanilla wafer cookie crumbs, light brown sugar, fine sea salt, and ground cinnamon. Add the chunks of unsalted butter and mix until the mixture resembles wet sand.
Press the crumb mixture evenly into the bottom and up the sides of a 9-inch tart pan. Pack it tightly to create a sturdy crust. Bake in the preheated oven for about 10 minutes, or until golden brown. Remove from the oven and let it cool completely.
In a small saucepan, gently heat the dulce de leche over low heat. If it’s too thick, add 2-4 tablespoons of heavy cream, stirring until smooth and pourable. Pour the dulce de leche into the cooled tart crust, spreading it evenly.
Using a double boiler or microwave, melt the finely chopped dark chocolate with 1/4 cup of heavy whipping cream. Stir until completely smooth. In a separate bowl, whip the remaining 1 cup of heavy whipping cream until stiff peaks form. Gently fold the melted chocolate mixture into the whipped cream until fully combined.
Pour the chocolate filling over the dulce de leche layer in the tart crust, smoothing it out with a spatula. Place the tart in the refrigerator to set for at least 2 hours, or until firm.
Once set, remove the tart from the refrigerator. Just before serving, sprinkle the top with flake sea salt. Slice and enjoy this delightful tart!