Start by mixing flour and powdered sugar in a bowl. Add cold butter and cut it into the dry ingredients until the mixture resembles coarse crumbs. Add the egg yolk and ice water, mixing until a dough forms. Press the dough into your tart pans and refrigerate for 30 minutes. Preheat your oven to 350°F (175°C) and bake the crusts for 15 to 20 minutes, or until golden brown. Let them cool completely.

In a saucepan over medium heat, melt the sugar while stirring occasionally until it turns a rich amber color. Carefully whisk in the heavy cream—be cautious of bubbling. Add the butter and stir until smooth. Remove from heat and mix in the vanilla extract and sea salt. Set aside to cool slightly.

Heat the cream in a saucepan until it just begins to simmer. Pour it over the chocolate chips in a heatproof bowl. Let it sit for 2 minutes, then stir until the ganache is silky and smooth.

Spoon the cooled caramel into each tart shell, filling them halfway. Chill the tarts for 20 to 30 minutes until the caramel sets. Then, pour the chocolate ganache on top of the caramel layer. Finish with a sprinkle of flaky sea salt. Refrigerate for at least 2 hours before serving to let everything set beautifully.