Instructions

• Make the crust: In a food processor, combine 10 tablespoons softened unsalted butter and 2/3 cup (80 g) powdered sugar. Process until pale in color, about 10 seconds.
• Add 1/3 cup (28.67 g) Dutch-process cocoa powder, 1½ cups (187.5 g) all-purpose flour, 2 egg yolks, and 1 teaspoon vanilla extract. Pulse in short 1-second bursts (about 10 pulses) until a soft dough forms.
• Turn the dough out into a 9-inch tart pan. Press the dough evenly into the bottom and up the sides of the pan. Smooth the surface. Refrigerate until firm, at least 30 minutes.
• Preheat the oven to 350°F (175°C). Remove the chilled tart shell from the refrigerator and prick the bottom all over with a fork.
• Bake the crust for 15 minutes, or until the crust is set and firm to the touch. Remove from the oven and let the crust cool to room temperature.
• Make the caramel filling: In a small saucepan, combine 3/4 cup (178.5 ml) heavy cream and 6 tablespoons unsalted butter. Warm over low heat until the butter has melted, then remove from the heat and keep warm.
• In a medium saucepan, combine 1½ cups (300 g) superfine sugar and 1/2 cup (125 ml) water. Cook over low heat, stirring only until the sugar dissolves.
• Increase the heat to high and boil the sugar mixture without stirring until it turns dark golden and reaches 340°F on a candy thermometer. (Do not stir while boiling.)
• Remove the saucepan from the heat and, very slowly, whisk in the warm cream-and-butter mixture (the mixture will bubble vigorously). When incorporated, return the pan to low heat and cook, stirring constantly, for 5 minutes or until the caramel has thickened.
• Stir in 1/2 teaspoon fleur de sel. Pour the hot caramel into the cooled pastry shell and spread evenly. Refrigerate until the caramel is set, at least 30 minutes.
• Make the chocolate glaze: Place 5 ounces (141.75 g) finely chopped dark chocolate in a medium bowl. In a small saucepan, heat 1/2 cup (119 ml) heavy cream over medium heat until it just begins to simmer. Remove from the heat and pour the hot cream over the chopped chocolate.
• Let the chocolate and cream sit undisturbed for 2 minutes, then stir until smooth and glossy.
• Pour the chocolate glaze over the set caramel layer and spread evenly. Refrigerate until the chocolate is set, at least 15 minutes.
• Sprinkle additional fleur de sel to garnish before serving.
• Store leftovers covered in the refrigerator for up to 5 days.