Preheat oven to 350°F (175°C). In a mixing bowl, combine flour, powdered sugar, and salt. Add cold, cubed butter and mix until crumbly. Add egg yolk and mix until dough forms. Press dough into a tart pan. Bake for 15-20 minutes or until golden brown. Let cool.
In a saucepan, melt granulated sugar over medium heat until it turns amber. Add butter and stir until melted. Slowly add heavy cream and sea salt, stirring constantly. Let cool slightly before pouring into the cooled crust. Refrigerate until set.
Heat heavy cream in a saucepan until just boiling. Pour over chopped dark chocolate and let sit for a minute. Stir until smooth. Pour over the set caramel layer. Refrigerate until ganache is firm.