Mix the crushed cookies with 3 tablespoons of melted butter until the crumbs hold together. Press the mixture evenly into four small tartlet pans and chill for 15 minutes to set the crust.

Place the sugar in a saucepan over medium heat. Stir until it melts into a golden caramel. Add the remaining 2 tablespoons of butter and stir until smooth.

Slowly pour in ½ cup of the heavy cream while stirring. The mixture will bubble. Continue cooking for 2 minutes, then remove from heat and stir in the vanilla and ½ teaspoon of the smoked sea salt. Let the caramel cool for 5 minutes.

Divide the warm caramel among the chilled crusts and spread it into an even layer. Return the tartlets to the refrigerator for 20 minutes.

Heat the remaining ½ cup of heavy cream until it just begins to steam. Pour it over the chopped dark chocolate and let it sit for 1 minute, then stir until the chocolate melts into a glossy ganache.

Spoon the ganache over the caramel layer in each tartlet. Sprinkle the tops with the remaining ¼ teaspoon of smoked sea salt. Chill for at least 1 hour before serving.